https://leetcode.cn/problems/binary-search/
简单二分
class Solution {
public:
int search(vector<int>& nums, int target) {
int l=0,r=nums.size()-1;
while(l<r)
{
int mid=l+r>>1;
if(nums[mid]>=target)r=mid;
else l=mid+1;
}
if(nums[l]!=target)return -1;
return l;
}
};