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.