LeetCode[202] Happy Number

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

1^2 + 9^2 = 82

8^2 + 2^2 = 68

6^2 + 8^2 = 100

1^2 + 0^2 + 0^2 = 1

分析:

这题找到规律后就简单了。如果右边的出现了某个重复的数,但不是1,说明会无限循环下去,这个数就不是快乐数,如果是1,则是快乐数。

代码:

public class Solution {
public boolean isHappy(int n) {
Set<Integer> existed = new HashSet<Integer>();
while(true){
int sum = 0;
while (n > 0){
int digit = n % 10;
sum += digit * digit;
n /= 10;
}
if(existed.contains(sum)){
return sum == 1;
}else{
existed.add(sum);
}
n = sum;
}
}
}

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