Leetcode202 Happy number

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DescriptionWrite 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.

Input: 19

Output: true

【Leetcode202 Happy number】Explanation:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

Analysis判断环的两大方法
Hashset

class Solution { public: bool isHappy(int n) { while(n!=1){ n=process(n); if(a[n]==1)return 0; a[n]=1; } return 1; } private: int process(int x){ int sum=0; while(x!=0){ int u=x%10; sum+=u*u; x/=10; } return sum; } int a[50000]; };

龟兔赛跑法

文章图片

设定两个指针，一快一慢，快的一次走2步，慢的一次走1步
Code

class Solution { public: bool isHappy(int n) { int a=n,b=n; while(a!=1){ a=process(a); a=process(a); b=process(b); if(a==b)break; } return a==1; } private: int process(int x){ int sum=0; while(x!=0){ int u=x%10; sum+=u*u; x/=10; } return sum; } };