一個小小工程師的心情抒發天地

這一題比較難的地方是把規則看懂, 以及想辦法把數字拆開來, 簡單運用%和/就可以拆開了, 這會是想得比較久的地方; 本來還想試試看用Recusion的方式來做, 不過似乎是太久沒有寫這玩意.... 我完全腦袋一片空白..; 所以, 如果有人有寫出來的, 也歡迎寫信給我, 讓我知道一下各位的想法囉:D

Write 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.
• 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.

Return true if n is a happy number, and false if not.

Example 1:

Input: n = 19
Output: true
Explanation:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

Example 2:

Input: n = 2
Output: false

Constraints:

• 1 <= n <= 231 - 1

int cal(int n) {
    int x = n;
    int s = 0;
    while (x > 0) {
        s = s + (x % 10)*(x % 10);
        x = x / 10;
    }
    return s;
}

bool isHappy(int n)
{
    int x = n;
    int y = n;
    while (x > 1) {
        x = cal(x);
        if (x == 1)return true;
        y = cal(cal(y));
        if (y == 1)return true;

        if (x == y)return false;
    }
    return true;
}