LeetCode (24) Happy Number

標籤：leetcode   演算法   c++   

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

• 12+92=82
• 82+22=68
• 62+82=100

本題比較簡單，題目要求對任意一個正整數，不斷各個數位上數位平方和，若最終收斂為1，則該數字為happy number，否則程式可能從某個數開始陷入迴圈。這道題目我們只用根據規則進行計算，並使用一個雜湊表儲存已經出現過的數字即可。

class Solution {public:    bool isHappy(int n) {        if (n < 1)            return false;        if (n == 1)            return true;        unordered_set<int> showedNums;        showedNums.insert(n);        while(true)        {            int s = 0;            while(n)            {                s += (n % 10) * (n % 10);                n = n / 10;            }            if (s == 1)                return true;            else if (showedNums.find(s) != showedNums.end())                return false;            n = s;            showedNums.insert(s);        }    }};

LeetCode (24) Happy Number