LeetCode -- Valid Perfect Square

题目描述：

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

本题属于数学分类。
思路：

任意完全平方数可通过1+3+5...+K的和得到。

实现代码：

public class Solution {
public bool IsPerfectSquare(int num) {
var start = 1;

while(num > 0){
num -= start;
start += 2;
}

return num == 0;
}
}