题目连接
https://leetcode.com/problems/valid-perfect-square/
Valid Perfect Square
Description
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 Returns: True
Example 2:
Input: 14 Returns: False
二分
class Solution {
public:
bool isPerfectSquare(int num) {
int lb = 1, ub = 92682;
while(lb <= ub) {
int m = (lb + ub) >> 1;
long long v = (long long)m * m;
if(v == num) return true;
if(v > num) ub = m - 1;
else lb = m + 1;
}
return false;
}
};