開心數字

原題

　　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

 

 

題目大意

　　對任意一個正整數，不斷求個數位上數字的平方和，若最終收斂爲1，則該數字爲happy number，不然程序可能從某個數開始陷入循環。

解題思路

　　對這個數字的每一個數位求平方和，若是如和爲1或者平方和是以前出現過的就不進行求和，根據最後的結果判斷是否是一個開心數字。

代碼實現

算法實現類

mport java.util.HashSet;

public class Solution {
    public boolean isHappy(int n) {
        if (n < 1) {
            return false;
        }

        // 用於保存中間出現的結果
        HashSet<Integer> set = new HashSet<>(32);

        int tmp;
        int newN;

        // n不爲1，而且n的值不能重複出現，不然會死循環
        while (n != 1 && !set.contains(n)) {
            set.add(n);
            newN = 0;
            while (n > 0) {
                tmp = n % 10;
                n /= 10;
                newN += tmp * tmp;
            }

            n = newN;
        }

        return n == 1;
    }
}