Leetcode——第367题完全平均数

也使用二分法

class Solution {
public:
    bool isPerfectSquare(int num) {
        int l=0,r=num;
        while(l<=r){
            int mid=l+(r-l)/2;
            if((long long)mid*mid==num) return true;
            if((long long)mid*mid<num){
                l=mid+1;
            }
            else r=mid-1;
        }
        return false;
    }
};