leetcode704基本二分查找

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