Happy Number 分类： Leetcode（查找） 2015-07-17 10:00 2人阅读 评论(0) 收藏

1. 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

• 1 2 + 9 2 = 82
• 8 2 + 2 2 = 68
• 6 2 + 8 2 = 100
• 1 2 + 0 2 + 0 2 = 1

简单的水题，用hash表去判断有无重复。一个巧妙的解题思路是，对于循环重复的情况，可以用slow和fast两个变量来代替hash表。

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

class Solution {
public:

    int cal(int n){
        int s = 0;
        while(n){
            s +=(n%10)*(n%10);
            n /= 10;
        }
        return s;
    }
    bool isHappy(int n) {
        if (n < 1)
            return false;
        if (n == 1)
            return true;
        int slow=n,fast=n;
        do {
            slow = cal(slow);
            fast = cal(fast);
            fast = cal(fast);
        }while(slow != fast);
        if(slow ==1) return 1;
        else return 0;
        
        
    }
};

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