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Commit c27939d

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LeetCode problem: 704. Binary Search
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# 704. Binary Search
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Difficulty: `Easy`
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Topics: `Array`, `Binary Search`
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Given an array of integers `nums` which is sorted in ascending order, and an integer `target`, write a function to
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search `target` in `nums`. If `target` exists, then return its index. Otherwise, return `-1`.
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You must write an algorithm with `O(log n)` runtime complexity.
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**Example 1:**
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```text
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Input: nums = [-1,0,3,5,9,12], target = 9
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Output: 4
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Explanation: 9 exists in nums and its index is 4
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```
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**Example 2:**
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```text
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Input: nums = [-1,0,3,5,9,12], target = 2
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Output: -1
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Explanation: 2 does not exist in nums so return -1
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```
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**Constraints:**
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- `1 <= nums.length <= 10^4`
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- `-10^4 < nums[i], target < 10^4`
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- All the integers in `nums` are unique.
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- `nums` is sorted in ascending order.
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package com.bl.binary_search;
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/**
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* This is the solution to the LeetCode problem: 704. Binary Search
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*
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* @author Børre A. Opedal Lunde
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* @since 2024年01月27日
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*/
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public class Solution {
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public int search(int[] nums, int target) {
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int low = 0;
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int high = nums.length - 1;
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// The loop will continue until the target is found or the low and high
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// indices have crossed each other. In which the target was not found.
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while (low <= high) {
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// The reason why we don't use (low + high) / 2 is because it can
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// cause an integer overflow. For example:
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// low = 2 000 000 000
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// high = 2 000 000 000
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// low + high = 4 000 000 000 which is larger than the maximum
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// integer value: 2 147 483 647
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final int middleIndex = low + (high - low) / 2;
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final int middleValue = nums[middleIndex];
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if (middleValue == target) {
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// The target was found, return its index.
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return middleIndex;
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} else if (middleValue > target) {
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// The target must be in the left half (lower half) of the array.
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high = middleIndex - 1;
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} else {
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// The target must be in the right half (upper half) of the array.
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low = middleIndex + 1;
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}
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}
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// -1 represents that the target was not found.
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return - 1;
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}
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}
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package com.bl.binary_search;
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import org.junit.jupiter.api.DisplayName;
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import org.junit.jupiter.api.Test;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertTrue;
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/**
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* This is the test to the LeetCode problem: 704. Binary Search
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*
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* @author Børre A. Opedal Lunde
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* @since 2024年01月27日
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*/
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@DisplayName("Binary Search")
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class SolutionTest {
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private final Solution solution = new Solution();
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@Test
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@DisplayName("Example one")
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void exampleOne() {
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int[] nums = {- 1, 0, 3, 5, 9, 12};
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int target = 9;
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int expected = 4;
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int actual = solution.search(nums, target);
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assertEquals(expected, actual);
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}
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@Test
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@DisplayName("Example two")
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void exampleTwo() {
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int[] nums = {- 1, 0, 3, 5, 9, 12};
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int target = 2;
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int expected = - 1;
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int actual = solution.search(nums, target);
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assertEquals(expected, actual);
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}
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@Test
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@DisplayName("Empty array should return -1")
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void emptyArrayShouldReturn1() {
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int[] nums = {};
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int target = 9; // Doesn't matter what the target is.
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int expected = - 1;
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int actual = solution.search(nums, target);
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assertEquals(expected, actual);
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}
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@Test
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@DisplayName("Target is a negative number")
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void targetIsANegativeNumber() {
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int[] nums = {- 1, 0, 3, 5, 9, 12};
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int target = - 1;
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int expected = 0;
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int actual = solution.search(nums, target);
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assertEquals(expected, actual);
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}
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@Test
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@DisplayName("Target is larger than the largest number in the array")
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void targetIsLargerThanTheLargestNumberInTheArray() {
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int[] nums = {- 1, 0, 3, 5, 9, 12};
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int target = 13;
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int expected = - 1;
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int actual = solution.search(nums, target);
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assertEquals(expected, actual);
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}
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@Test
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@DisplayName("Target is smaller than the smallest number in the array")
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void targetIsSmallerThanTheSmallestNumberInTheArray() {
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int[] nums = {- 1, 0, 3, 5, 9, 12};
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int target = - 2;
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int expected = - 1;
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int actual = solution.search(nums, target);
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assertEquals(expected, actual);
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}
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@Test
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@DisplayName("All elements in the array are the same")
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void allElementsInTheArrayAreTheSame() {
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int[] nums = {1, 1, 1, 1, 1, 1};
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int target = 1;
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int actual = solution.search(nums, target);
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// The actual index is not important, as long as it's a valid index.
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assertTrue(actual >= 0 && nums[actual] == target);
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}
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}

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