367. Valid Perfect Square

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

 

Approach #1:

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

　　

Runtime: 0 ms, faster than 100.00% of C++ online submissions for Valid Perfect Square.

 

 Analysis:

If use int type it will report error.