【leetcode】367. Valid Perfect Square【M】【35】

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: 16Returns: True

Example 2:

Input: 14Returns: False

Credits:
Special thanks to @elmirap for adding this problem and creating all test cases.

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最开始的想法是，从1~num/2挨个枚举，看看有没有是它的平方的，后来一想，直接挨个算，算到平方超过这个数，就结束。。

class Solution(object):def isPerfectSquare(self, num):i = 1#res = 1while 1:#i <= num:#print resres = i**2if res > num:    return Falseif res == num:return Truei += 1#res += i+i-1return False