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Commit f014f4a

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Added tasks 404-406.
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package g0401_0500.s0404_sum_of_left_leaves;
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// #Easy #Depth_First_Search #Breadth_First_Search #Tree #Binary_Tree
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import com_github_leetcode.TreeNode;
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import java.util.ArrayList;
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import java.util.List;
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/*
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* Definition for a binary tree node.
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* public class TreeNode {
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* int val;
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* TreeNode left;
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* TreeNode right;
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* TreeNode() {}
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* TreeNode(int val) { this.val = val; }
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* TreeNode(int val, TreeNode left, TreeNode right) {
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* this.val = val;
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* this.left = left;
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* this.right = right;
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* }
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* }
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*/
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public class Solution {
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public int sumOfLeftLeaves(TreeNode root) {
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List<Integer> arr = new ArrayList<>();
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traverse(root, arr);
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return getSum(arr);
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}
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private void traverse(TreeNode root, List<Integer> arr) {
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if (root == null) {
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return;
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}
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if (root.left != null && root.left.left == null && root.left.right == null) {
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arr.add(root.left.val);
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}
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traverse(root.left, arr);
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traverse(root.right, arr);
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}
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private int getSum(List<Integer> arr) {
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int sum = 0;
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for (int i = 0; i < arr.size(); i++) {
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sum += arr.get(i);
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}
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return sum;
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}
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}
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404\. Sum of Left Leaves
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Easy
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Given the `root` of a binary tree, return the sum of all left leaves.
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**Example 1:**
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![](https://assets.leetcode.com/uploads/2021/04/08/leftsum-tree.jpg)
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**Input:** root = \[3,9,20,null,null,15,7\]
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**Output:** 24
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**Explanation:** There are two left leaves in the binary tree, with values 9 and 15 respectively.
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**Example 2:**
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**Input:** root = \[1\]
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**Output:** 0
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**Constraints:**
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* The number of nodes in the tree is in the range `[1, 1000]`.
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* `-1000 <= Node.val <= 1000`
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package g0401_0500.s0405_convert_a_number_to_hexadecimal;
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// #Easy #Math #Bit_Manipulation
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public class Solution {
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public String toHex(int num) {
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if (num == 0) {
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return "0";
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}
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StringBuilder sb = new StringBuilder();
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int x;
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while (num != 0) {
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x = num & 0xf;
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if (x < 10) {
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sb.append(x);
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} else {
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sb.append((char) (x + 87));
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}
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num = num >>> 4;
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}
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return sb.reverse().toString();
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}
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}
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405\. Convert a Number to Hexadecimal
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Easy
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Given an integer `num`, return _a string representing its hexadecimal representation_. For negative integers, [two’s complement](https://en.wikipedia.org/wiki/Two%27s_complement) method is used.
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All the letters in the answer string should be lowercase characters, and there should not be any leading zeros in the answer except for the zero itself.
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**Note:** You are not allowed to use any built-in library method to directly solve this problem.
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**Example 1:**
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**Input:** num = 26
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**Output:** "1a"
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**Example 2:**
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**Input:** num = -1
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**Output:** "ffffffff"
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**Constraints:**
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* <code>-2<sup>31</sup> <= num <= 2<sup>31</sup> - 1</code>
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package g0401_0500.s0406_queue_reconstruction_by_height;
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// #Medium #Array #Sorting #Greedy
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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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public class Solution {
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public int[][] reconstructQueue(int[][] people) {
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Arrays.sort(people, (a, b) -> a[0] != b[0] ? -a[0] + b[0] : a[1] - b[1]);
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List<int[]> res = new ArrayList<>();
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for (int[] a : people) {
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res.add(a[1], a);
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}
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return res.toArray(new int[people.length][]);
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}
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}
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406\. Queue Reconstruction by Height
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Medium
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You are given an array of people, `people`, which are the attributes of some people in a queue (not necessarily in order). Each <code>people[i] = [h<sub>i</sub>, k<sub>i</sub>]</code> represents the <code>i<sup>th</sup></code> person of height <code>h<sub>i</sub></code> with **exactly** <code>k<sub>i</sub></code> other people in front who have a height greater than or equal to <code>h<sub>i</sub></code>.
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Reconstruct and return _the queue that is represented by the input array_ `people`. The returned queue should be formatted as an array `queue`, where <code>queue[j] = [h<sub>j</sub>, k<sub>j</sub>]</code> is the attributes of the <code>j<sup>th</sup></code> person in the queue (`queue[0]` is the person at the front of the queue).
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**Example 1:**
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**Input:** people = \[\[7,0\],\[4,4\],\[7,1\],\[5,0\],\[6,1\],\[5,2\]\]
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**Output:** \[\[5,0\],\[7,0\],\[5,2\],\[6,1\],\[4,4\],\[7,1\]\]
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**Explanation:**
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Person 0 has height 5 with no other people taller or the same height in front.
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Person 1 has height 7 with no other people taller or the same height in front.
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Person 2 has height 5 with two persons taller or the same height in front, which is person 0 and 1.
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Person 3 has height 6 with one person taller or the same height in front, which is person 1.
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Person 4 has height 4 with four people taller or the same height in front, which are people 0, 1, 2, and 3.
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Person 5 has height 7 with one person taller or the same height in front, which is person 1.
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Hence [[5,0],[7,0],[5,2],[6,1],[4,4],[7,1]] is the reconstructed queue.
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**Example 2:**
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**Input:** people = \[\[6,0\],\[5,0\],\[4,0\],\[3,2\],\[2,2\],\[1,4\]\]
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**Output:** \[\[4,0\],\[5,0\],\[2,2\],\[3,2\],\[1,4\],\[6,0\]\]
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**Constraints:**
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* `1 <= people.length <= 2000`
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* <code>0 <= h<sub>i</sub> <= 10<sup>6</sup></code>
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* <code>0 <= k<sub>i</sub> < people.length</code>
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* It is guaranteed that the queue can be reconstructed.
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package g0401_0500.s0404_sum_of_left_leaves;
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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 com_github_leetcode.TreeNode;
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import java.util.Arrays;
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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 sumOfLeftLeaves() {
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assertThat(
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new Solution()
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.sumOfLeftLeaves(
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TreeNode.create(Arrays.asList(3, 9, 20, null, null, 15, 7))),
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equalTo(24));
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}
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@Test
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void sumOfLeftLeaves2() {
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assertThat(new Solution().sumOfLeftLeaves(TreeNode.create(Arrays.asList(1))), equalTo(0));
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}
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}
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package g0401_0500.s0405_convert_a_number_to_hexadecimal;
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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 toHex() {
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assertThat(new Solution().toHex(26), equalTo("1a"));
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}
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@Test
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void toHex2() {
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assertThat(new Solution().toHex(-1), equalTo("ffffffff"));
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}
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}
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package g0401_0500.s0406_queue_reconstruction_by_height;
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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 reconstructQueue() {
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assertThat(
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new Solution()
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.reconstructQueue(
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new int[][] {{7, 0}, {4, 4}, {7, 1}, {5, 0}, {6, 1}, {5, 2}}),
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equalTo(new int[][] {{5, 0}, {7, 0}, {5, 2}, {6, 1}, {4, 4}, {7, 1}}));
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}
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@Test
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void reconstructQueue2() {
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assertThat(
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new Solution()
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.reconstructQueue(
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new int[][] {{6, 0}, {5, 0}, {4, 0}, {3, 2}, {2, 2}, {1, 4}}),
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equalTo(new int[][] {{4, 0}, {5, 0}, {2, 2}, {3, 2}, {1, 4}, {6, 0}}));
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}
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}

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