LeetCode-in-Java
367. Valid Perfect Square
Easy
Given a positive integer num, write a function which returns True if num is a perfect square else False.
Follow up: Do not use any built-in library function such as sqrt.
Example 1:
Input: num = 16
Output: true
Example 2:
Input: num = 14
Output: false
Constraints:
1 <= num <= 2^31 - 1
Solution
public class Solution {
public boolean isPerfectSquare(int num) {
if (num == 0) {
// If num is 0 return false
return false;
}
// long datatype can holds huge number.
long start = 0;
long end = num;
long mid;
while (start <= end) {
// until start is lesser or equal to end do this
// Finding middle value
mid = start + (end - start) / 2;
if (mid * mid == num) {
// if mid*mid == num return true
return true;
} else if (mid * mid < num) {
// if num is greater than mid*mid then make start = mid + 1
start = mid + 1;
} else if (mid * mid > num) {
// if num is lesser than mid*mid then make end = mid - 1
end = mid - 1;
}
}
return false;
}
}