leetcode: (202) Happy Number

【Question】

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

方法一：Happy number容易判断，关键是要确定不是happy number的数，不是的话会一直循环下去，得到的中间值也是循环下去的；

因此，将每次得到的中间结果存起来，如果得到的中间结果与存起来的值有相等的话，就不是happy number

class Solution {public:  bool isHappy(int n)  { int result; vector<int> temp; while(true) { temp.push_back(n); result=0;        while(n>0){result+=(n%10)*(n%10);n/=10;}if (result==1) return true;else n=(int)result;for(int i=0;i<temp.size();i++){if (temp[i]==n) return false;} }      }};           

Runtime: 4 ms

方法二：利用hashset，当存入的元素与容器里面的相同时就认为不是happy number

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

Runtime: 284 ms