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

Note:Be careful about the overflow when multiple two integers

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public class Solution { public boolean isPerfectSquare(int num) { int l=0,r=num/2+1;//for num=1, for num=4. it is a waste of calculation after the 4. //but as a general approach, this keeps code concise while(l<=r){ int m = l+(r-l)/2; long ans = (long)m*(long)m;//overflow if(ans==num)return true; if(ans>num)r=m-1; if(ans<num)l=m+1; } return false; } }