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LeetCode:Valid Perfect Square

来源：程序员人生发布时间：2016-06-30 16:15:17 阅读次数：2401次

Valid Perfect Square

Total Accepted: 1976 Total Submissions: 5317 Difficulty: Medium

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

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

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(M) Sqrt(x)

思路：

2分查找。

java code:

public class Solution { public boolean isPerfectSquare(int num) { long lo = 1, hi = num / 2; if(num == 1) return true; long x = num; while(lo <= hi) { long mid = lo + (hi - lo) / 2; if(mid * mid == x) return true; else if(mid * mid < x) lo = mid + 1; else hi = mid - 1; } return false; } }

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