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Commit 909f90b

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Added tasks 374, 378, 380.
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package g0301_0400.s0374_guess_number_higher_or_lower;
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// #Easy #Binary_Search #Interactive
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/**
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* Forward declaration of guess API.
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*
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* @param num your guess
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* @return -1 if num is lower than the guess number 1 if num is higher than the guess number
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* otherwise return 0 int guess(int num);
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*/
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public class Solution {
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public int guessNumber(int n) {
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int left = 1;
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int right = n;
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int mid;
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while (left <= right) {
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mid = left + (right - left) / 2;
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if (guess(mid) == 1) {
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left = mid + 1;
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} else if (guess(mid) == -1) {
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right = mid - 1;
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} else {
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return mid;
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}
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}
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return -1;
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}
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// Assume we pick 7
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private int guess(int num) {
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return Integer.compare(7, num);
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}
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}
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374\. Guess Number Higher or Lower
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Easy
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We are playing the Guess Game. The game is as follows:
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I pick a number from `1` to `n`. You have to guess which number I picked.
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Every time you guess wrong, I will tell you whether the number I picked is higher or lower than your guess.
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You call a pre-defined API `int guess(int num)`, which returns 3 possible results:
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* `-1`: The number I picked is lower than your guess (i.e. `pick < num`).
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* `1`: The number I picked is higher than your guess (i.e. `pick > num`).
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* `0`: The number I picked is equal to your guess (i.e. `pick == num`).
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Return _the number that I picked_.
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**Example 1:**
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**Input:** n = 10, pick = 6
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**Output:** 6
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**Example 2:**
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**Input:** n = 1, pick = 1
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**Output:** 1
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**Example 3:**
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**Input:** n = 2, pick = 1
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**Output:** 1
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**Example 4:**
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**Input:** n = 2, pick = 2
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**Output:** 2
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**Constraints:**
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* <code>1 <= n <= 2<sup>31</sup> - 1</code>
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* `1 <= pick <= n`
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package g0301_0400.s0378_kth_smallest_element_in_a_sorted_matrix;
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// #Medium #Top_Interview_Questions #Array #Sorting #Binary_Search #Matrix #Heap_Priority_Queue
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public class Solution {
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public int kthSmallest(int[][] matrix, int k) {
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if (matrix == null || matrix.length == 0) {
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return -1;
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}
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int start = matrix[0][0];
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int end = matrix[matrix.length - 1][matrix[0].length - 1];
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// O(log(max-min)) time
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while (start + 1 < end) {
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int mid = start + (end - start) / 2;
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if (countLessEqual(matrix, mid) < k) {
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// look towards end
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start = mid;
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} else {
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// look towards start
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end = mid;
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}
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}
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// leave only with start and end, one of them must be the answer
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// try to see if start fits the criteria first
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if (countLessEqual(matrix, start) >= k) {
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return start;
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} else {
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return end;
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}
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}
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// countLessEqual
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// O(n) Time
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private int countLessEqual(int[][] matrix, int target) {
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// binary elimination from top right
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int row = 0;
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int col = matrix[0].length - 1;
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int count = 0;
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while (row < matrix.length && col >= 0) {
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if (matrix[row][col] <= target) {
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// get the count in current row
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count += col + 1;
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row++;
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} else if (matrix[row][col] > target) {
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// eliminate the current col
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col--;
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}
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}
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return count;
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}
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}
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378\. Kth Smallest Element in a Sorted Matrix
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Medium
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Given an `n x n` `matrix` where each of the rows and columns is sorted in ascending order, return _the_ <code>k<sup>th</sup></code> _smallest element in the matrix_.
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Note that it is the <code>k<sup>th</sup></code> smallest element **in the sorted order**, not the <code>k<sup>th</sup></code> **distinct** element.
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You must find a solution with a memory complexity better than <code>O(n<sup>2</sup>)</code>.
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**Example 1:**
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**Input:** matrix = \[\[1,5,9\],\[10,11,13\],\[12,13,15\]\], k = 8
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**Output:** 13
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**Explanation:** The elements in the matrix are \[1,5,9,10,11,12,13,**13**,15\], and the 8<sup>th</sup> smallest number is 13
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**Example 2:**
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**Input:** matrix = \[\[-5\]\], k = 1
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**Output:** -5
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**Constraints:**
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* `n == matrix.length == matrix[i].length`
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* `1 <= n <= 300`
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* <code>-10<sup>9</sup> <= matrix[i][j] <= 10<sup>9</sup></code>
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* All the rows and columns of `matrix` are **guaranteed** to be sorted in **non-decreasing order**.
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* <code>1 <= k <= n<sup>2</sup></code>
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**Follow up:**
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* Could you solve the problem with a constant memory (i.e., `O(1)` memory complexity)?
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* Could you solve the problem in `O(n)` time complexity? The solution may be too advanced for an interview but you may find reading [this paper](http://www.cse.yorku.ca/~andy/pubs/X+Y.pdf) fun.
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package g0301_0400.s0380_insert_delete_getrandom_o1;
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// #Medium #Top_Interview_Questions #Array #Hash_Table #Math #Design #Randomized
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import java.security.SecureRandom;
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.List;
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import java.util.Map;
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public class RandomizedSet {
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private final SecureRandom rand;
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private final List<Integer> list;
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private final Map<Integer, Integer> map;
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// Initialize your data structure here.
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public RandomizedSet() {
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this.rand = new SecureRandom();
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this.list = new ArrayList<>();
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this.map = new HashMap<>();
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}
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// Inserts a value to the set. Returns true if the set did not already contain the specified
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// element.
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public boolean insert(int val) {
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if (this.map.containsKey(val)) {
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return false;
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}
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this.list.add(val);
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this.map.put(val, list.size() - 1);
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return true;
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}
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// Removes a value from the set. Returns true if the set contained the specified element.
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public boolean remove(int val) {
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if (!this.map.containsKey(val)) {
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return false;
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}
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int index = this.map.get(val);
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if (index == this.list.size() - 1) {
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this.list.remove(index);
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this.map.remove(val);
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return true;
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}
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int value = list.get(list.size() - 1);
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this.list.set(index, value);
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this.list.remove(this.list.size() - 1);
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this.map.remove(val);
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this.map.put(value, index);
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return true;
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}
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// Get a random element from the set.
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public int getRandom() {
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return this.list.get(rand.nextInt(list.size()));
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}
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}
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/*
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* Your RandomizedSet object will be instantiated and called as such: RandomizedSet obj = new
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* RandomizedSet(); boolean param_1 = obj.insert(val); boolean param_2 = obj.remove(val); int
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* param_3 = obj.getRandom();
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*/
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380\. Insert Delete GetRandom O(1)
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Medium
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Implement the `RandomizedSet` class:
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* `RandomizedSet()` Initializes the `RandomizedSet` object.
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* `bool insert(int val)` Inserts an item `val` into the set if not present. Returns `true` if the item was not present, `false` otherwise.
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* `bool remove(int val)` Removes an item `val` from the set if present. Returns `true` if the item was present, `false` otherwise.
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* `int getRandom()` Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the **same probability** of being returned.
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You must implement the functions of the class such that each function works in **average** `O(1)` time complexity.
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**Example 1:**
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**Input**
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\["RandomizedSet", "insert", "remove", "insert", "getRandom", "remove", "insert", "getRandom"\]
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\[\[\], \[1\], \[2\], \[2\], \[\], \[1\], \[2\], \[\]\]
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**Output:** \[null, true, false, true, 2, true, false, 2\]
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**Explanation:**
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RandomizedSet randomizedSet = new RandomizedSet();
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randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully.
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randomizedSet.remove(2); // Returns false as 2 does not exist in the set.
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randomizedSet.insert(2); // Inserts 2 to the set, returns true. Set now contains \[1,2\].
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randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly.
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randomizedSet.remove(1); // Removes 1 from the set, returns true. Set now contains \[2\].
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randomizedSet.insert(2); // 2 was already in the set, so return false.
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randomizedSet.getRandom(); // Since 2 is the only number in the set, getRandom() will always return 2.
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**Constraints:**
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* <code>-2<sup>31</sup> <= val <= 2<sup>31</sup> - 1</code>
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* At most `2 * `<code>10<sup>5</sup></code> calls will be made to `insert`, `remove`, and `getRandom`.
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* There will be **at least one** element in the data structure when `getRandom` is called.
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package g0301_0400.s0374_guess_number_higher_or_lower;
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import static org.hamcrest.CoreMatchers.equalTo;
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import static org.hamcrest.MatcherAssert.assertThat;
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import org.junit.jupiter.api.Test;
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class SolutionTest {
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@Test
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void guessNumber() {
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assertThat(new Solution().guessNumber(10), equalTo(7));
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}
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@Test
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void guessNumber2() {
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assertThat(new Solution().guessNumber(1), equalTo(-1));
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}
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@Test
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void guessNumber3() {
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assertThat(new Solution().guessNumber(2), equalTo(-1));
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}
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@Test
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void guessNumber4() {
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assertThat(new Solution().guessNumber(6), equalTo(-1));
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}
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}
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package g0301_0400.s0378_kth_smallest_element_in_a_sorted_matrix;
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import static org.hamcrest.CoreMatchers.equalTo;
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import static org.hamcrest.MatcherAssert.assertThat;
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import org.junit.jupiter.api.Test;
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class SolutionTest {
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@Test
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void kthSmallest() {
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assertThat(
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new Solution().kthSmallest(new int[][] {{1, 5, 9}, {10, 11, 13}, {12, 13, 15}}, 8),
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equalTo(13));
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}
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@Test
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void kthSmallest2() {
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assertThat(new Solution().kthSmallest(new int[][] {{-5}}, 1), equalTo(-5));
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}
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}
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package g0301_0400.s0380_insert_delete_getrandom_o1;
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import static org.hamcrest.CoreMatchers.equalTo;
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import static org.hamcrest.MatcherAssert.assertThat;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
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import org.junit.jupiter.api.Test;
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class RandomizedSetTest {
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@Test
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void randomizedSet() {
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List<String> result = new ArrayList<>();
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RandomizedSet randomizedSet = null;
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result.add(randomizedSet + "");
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randomizedSet = new RandomizedSet();
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result.add(randomizedSet.insert(1) + "");
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result.add(randomizedSet.remove(2) + "");
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result.add(randomizedSet.insert(2) + "");
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int random = randomizedSet.getRandom();
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result.add(random + "");
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result.add(randomizedSet.remove(1) + "");
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result.add(randomizedSet.insert(2) + "");
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result.add(randomizedSet.getRandom() + "");
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List<String> expected =
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new ArrayList<>(
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Arrays.asList("null", "true", "false", "true", "1", "true", "false", "2"));
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List<String> expected2 =
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new ArrayList<>(
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Arrays.asList("null", "true", "false", "true", "2", "true", "false", "2"));
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if (random == 1) {
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assertThat(result, equalTo(expected));
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} else {
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assertThat(result, equalTo(expected2));
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}
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}
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}

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