LeetCode - 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
Returns: True

Example 2:

Input: 14
Returns: False


binary search不过会产生 TLE：

class Solution {
    public boolean isPerfectSquare(int num) {
        int low = 0;
        int high = num;
        
        while(low <= high){
            int mid = (low+high)/2;
            int t = mid*mid;
            if(t == num){
                return true;
            }
            else if(t > num){
                high = mid-1;
            }
            else{
                low = mid+1;
            }
        }
        return false;
    }
}

class Solution {
    public boolean isPerfectSquare(int num) {
        for(int i=1; i<=num/i; i++){
            if(i*i == num){
                return true;
            }
        }
        return false;
    }
}