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
Output: true
Example 2:
Input: 14 Output: false
class Solution { public boolean isPerfectSquare(int num) { if(num == 1) return true; for(int i = 1; i <= num/2; i++){ if(i*i == num) return true; } return false; } }
brute force O(n/2)，慢
class Solution { public boolean isPerfectSquare(int num) { int i = 1; while (num > 0) { num -= i; i += 2; } return num == 0; } }
芜湖
原文：https://www.cnblogs.com/wentiliangkaihua/p/12861787.html