【leetcode刷题】T196-有效的完全平方数

示例 1：
输入：16
输出：True

示例 2：
输入：14
输出：False

class Solution(object):
    def isPerfectSquare(self, num):
        """
        :type num: int
        :rtype: bool
        """
        if num < 2:
            return True
        l, r = 1, num / 2
        while l <= r:
            mid = (l + r) / 2
            res = mid * mid
            if res == num:
                return True
            elif res < num:
                l = mid + 1
            else:
                r = mid - 1
        return False

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