704. 二分查找

class Solution {
public:
    int search(vector<int>& nums, int target) {
        
        int n = nums.size();
        int l = 0;
        int r = n-1;
        //在这个范围内进行查找，当然边界上的值也需要进行验证是否是
        //要找的数，所以这里的不等式为<=
        while(l <= r)
        {
            int mid = l + (r-l)/2;
            if(nums[mid] == target)
                return mid;
            else if(nums[mid] > target)
                r = mid-1;
            else
                l = mid+1;
        }
        return -1;
        
    }
};