暴力

class Solution {
public:bool isPerfectSquare(int num) {for(long i = 1; i * i <= num; i++) {if(i * i == num) return true;}return false;}
};

二分查找

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