367. 有效的完全平方数

题目

自己写的：

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

这题应该不算难，比69.x的平方根简单。

不过看了官方代码，自己的代码还有改进空间（即不用写多次(long long) mid * mid）：

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