leetcode 367. 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
Solution. An awesome solution is from here: n is perfect square if n = 1 + 3 + 5 + …. Below is the code:
public static boolean isPerfectSquare(int num) {
int delta = 1;
while (num > 0) {
num -= delta;
delta += 2;
}
return num == 0;
}