704. 二分查找

🟢   🔖  数组 二分查找  🔗 力扣 LeetCode

题目

Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1.

You must write an algorithm with O(log n) runtime complexity.

Example 1:

Input: nums = [-1,0,3,5,9,12], target = 9

Output: 4

Explanation: 9 exists in nums and its index is 4

Example 2:

Input: nums = [-1,0,3,5,9,12], target = 2

Output: -1

Explanation: 2 does not exist in nums so return -1

Constraints:

• 1 <= nums.length <= 10^4
• -104 < nums[i], target < 10^4
• All the integers in nums are unique.
• nums is sorted in ascending order.

题目大意

给定一个 n 个元素有序的（升序）整型数组 nums 和一个目标值 target ，写一个函数搜索 nums 中的 target，如果目标值存在返回下标，否则返回 -1。

解题思路

可以使用二分查找，要注意左右边界的赋值。

代码

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number}
 */
var search = function (nums, target) {
	let left = 0;
	let right = nums.length - 1;
	while (left <= right) {
		const mid = Math.floor((right + left) / 2);
		if (nums[mid] == target) {
			return mid;
		} else if (nums[mid] > target) {
			right = mid - 1;
		} else if (nums[mid] < target) {
			left = mid + 1;
		}
	}
	return -1;
};

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