leetcode_202题——Happy Number（哈希）

Happy Number

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Question Solution

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

Credits:
Special thanks to @mithmatt and @ts for adding this problem and creating all test cases.

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这道题将每次根据前一个值计算出来的结果储存在set中，再进行查找就可以了

#include<iostream>
//#include<map>
#include<set>
using namespace std;

int n_to_n(int a)
{
	int b=a;
	int last_result=0;

	while(b!=0)
	{
		last_result=(b%10)*(b%10)+last_result;
		b=b/10;
	}
	return last_result;
}

bool isHappy(int n) {
	set<int> temp;
	temp.insert(n);
	int a=n;
	bool c;
	while(1)
	{
		int b=n_to_n(a);
		if(b==1)
		{
			c=1;
			break;
		}
		if(temp.count(b)==1)
		{
			c=0;
			break;
		}
		temp.insert(b);
		cout<<b<<endl;
		a=b;
	}
	return c;
}
int main()
{
	cout<<isHappy(2)<<endl;
}