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Write an algorithm to determine if a number is "happy".
A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy numbers.
Example: 19 is a happy number
思路分析:这题比较简单,就是不断的做各个位置数字的平方加和操作,看是否会产生1。但是有一个地方要注意,就是怎么判断出现了循环,这里定义了一个Set,保存所有出现过的数字,对于计算得到的新的和,如果没有在Set中出现,就添加到Set中继续进行平方求和;否则,就是遇到了已经出现的数字,出现了循环,可以直接结束循环,返回false。
AC Code
public class Solution { public boolean isHappy(int n) { HashSet<Integer> appearedNums = new HashSet<Integer>(); while(!appearedNums.contains(n)){ appearedNums.add(n); int sum = 0; while(n != 0){ int digit = n % 10; n /= 10; sum += Math.pow(digit,2); } n = sum; if(sum == 1) return true; } return false; } }
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原文地址:http://blog.csdn.net/yangliuy/article/details/46286277