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leetcode筆記：Happy Number

編輯：關於C++

一. 題目描述

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 （各個位的平方和）
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1

二. 題目分析

題目要求對任意一個正整數，不斷各個數位上數字的平方和，若經過若干次運算後結果收斂到1，則該數字為Happy Number，不是Happy Number的數在經過多次運算後會從某個數開始陷入循環。這道題目我們只用根據規則進行計算，並使用一個map存儲已經出現過的數字，這樣每輪計算完成後查找map，若發現值已存在，證明已陷入循環，可跳出循環並判定該整數不是Happy Number。

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三. 示例代碼

#include 
#include

using namespace std;

class Solution
{
public:
    bool isHappy(int n)
    {
        if (n < 0) return false;
        if (n == 1) return true;

        map showNum;

        while (true)
        {
            int temp = 0;
            while (n)
            {
                temp += (n % 10) * (n % 10);
                n /= 10;
            }
            if (temp == 1)
                return true;
            else if (showNum[temp] == true) // 陷入循環，判為非快樂數
                return false;
            else
            {
                showNum[temp] = true;
                n = temp;
            }
        }
    }
};

一些測試結果：

這裡寫圖片描述