367. Valid Perfect Square*

367. Valid Perfect Square*

https://leetcode.com/problems/valid-perfect-square/

題目描述

Given a positive integer num, write a function which returns True if num is a perfect square else False.

Note: Do not use any built-in library function such as sqrt.

Example 1:

Input: 16
Output: true

Example 2:

Input: 14
Output: false

C++ 實現 1

題目不難, 只是需要考慮極端情況, 比如測試用例爲 num = 2147483647, 因此下面代碼中採用了 long long.

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