704. 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 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

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注意邊界條件即可 要考慮到left = right的情況

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