LeetCode:Valid Perfect Square

Posted 2020-07-31 walker lee

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.

Subscribe to see which companies asked this question

Hide Tags

 Binary Search

Hide Similar Problems

 (M) Sqrt(x)

思路：

二分查找。

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;
    }
}