704. Binary Search

Question

LeetCode Problem

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

Solutions

Use binary search

int search(vector<int>& nums, int target) {
	int left = 0;
	int right = static_cast<int>(nums.size() - 1);
	while (left <= right) {
		int mid = left + (right - left) / 2;
		if (nums[mid] == target) return mid;
		if (nums[mid] > target) {
			right = mid - 1;
		} else {
			left = mid + 1;
		}
	}
	return -1;
}