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
- 12 + 92 = 82
- 82 + 22 = 68
- 62 + 82 = 100
- 12 + 02 + 02 = 1
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;
}
}