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
题意:
验证完全平方数
思路:
二分查找,可回顾之前[leetcode]278. First Bad Version首个坏版本 笔记
需要注意的是类型声明为long
代码:
1 class Solution { 2 public boolean isPerfectSquare(int num) { 3 long left = 0; 4 long right = num; 5 6 while (left <= right) { 7 long mid = left + (right - left) / 2; 8 if (mid * mid == num) { 9 return true; 10 } else if (mid * mid < num) { 11 left = mid + 1; 12 } else { 13 right = mid - 1; 14 } 15 } 16 return false; 17 } 18 }