LeetCode 题解(200) : Happy Number

题目：

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

题解：

用一个Set或HashTable存已经出现的数。其他就是硬算了。

C++版：

class Solution {public:    bool isHappy(int n) {        unordered_set<int> s;        while(n != 1 && s.find(n) == s.end()) {            s.insert(n);            int temp = n;            n = 0;            while(temp != 0) {                int i = temp % 10;                n += i * i;                temp /= 10;            }        }        return n == 1;    }};

Java版：

import java.util.Hashtable;public class Solution {    public boolean isHappy(int n) {        Hashtable<Integer, Integer> s = new Hashtable<>();        while(n != 1 && !s.containsKey(n)) {            s.put(n, 1);            int temp = n;            n = 0;            while(temp != 0) {                int i = temp % 10;                n += i * i;                temp /= 10;            }        }        return n == 1;    }}

Python版：

class Solution(object):    def isHappy(self, n):        """        :type n: int        :rtype: bool        """        s = set()        while n != 1 and n not in s:            s.add(n)            n = sum([int(x) * int(x) for x in str(n)])        return n == 1