leetcode 30day--2

202. Happy Number

Write an algorithm to determine if a number n 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.

Return True if n is a happy number, and False if not.

Example: 

Input: 19
Output: true
Explanation: 
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

class Solution {
public:
    //主要是判断平方和是否会重复，如果重复就会造成cycle,否则就可以一直算下去，直到为1
    long help(int n){
        long res = 0;
        while(n){
            res += (n%10)*(n%10);
            n=n/10;
        }
        return res;
    }
    bool isHappy(int n) {
        if(n == 1){
            return true;
        }   
        if(m.find(n) != m.end()) return false;
        else{
            m[n] = true;
            return isHappy(help(n));
        }
    }
private:
    map<int,bool> m;
};

很巧妙，借鉴链表的快慢指针

class Solution {
public:
    //借鉴链表是否有环的快慢指针法
    long help(long n){
        long res=0;
        while(n){
            long tmp = n%10;
            n = n/10;
            res += tmp*tmp;
        }
        return res;
    }
    bool isHappy(int n) {
        long slow=n,fast=n;
        do{
            slow = help(slow);
            fast = help(fast);
            fast = help(fast);
            if(slow == 1 || fast == 1) return true;
        }while(slow != fast);
        
        return false;
    }
};