happy-number

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Algorithms

Write an algorithm to determine if a number <code>n</code> is happy.

A happy number is a number defined by the following process:

<ul>
	<li>Starting with any positive integer, replace the number by the sum of the squares of its digits.</li>
	<li>Repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1.</li>
	<li>Those numbers for which this process ends in 1 are happy.</li>
</ul>

Return <code>true</code> if <code>n</code> is a happy number, and <code>false</code> if not.

&nbsp;
Example 1:

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

Example 2:

<pre>
Input: n = 2
Output: false
</pre>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= n &lt;= 231 - 1</code></li>
</ul>

isHappy

Happy Number

Linked List Cycle

linked-list-cycle

环形链表

Add Digits

add-digits

各位相加

Ugly Number

ugly-number

丑数

Sum of Digits of String After Convert

sum-of-digits-of-string-after-convert

字符串转化后的各位数字之和

Minimum Addition to Make Integer Beautiful

minimum-addition-to-make-integer-beautiful

美丽整数的最小增量

Smallest Value After Replacing With Sum of Prime Factors

smallest-value-after-replacing-with-sum-of-prime-factors

使用质因数之和替换后可以取到的最小值

Count the Digits That Divide a Number

count-the-digits-that-divide-a-number

统计能整除数字的位数

Hash Table

Math

Two Pointers

编写一个算法来判断一个数 <code>n</code> 是不是快乐数。

「快乐数」&nbsp;定义为：

<ul>
	<li>对于一个正整数，每一次将该数替换为它每个位置上的数字的平方和。</li>
	<li>然后重复这个过程直到这个数变为 1，也可能是 无限循环 但始终变不到 1。</li>
	<li>如果这个过程 结果为&nbsp;1，那么这个数就是快乐数。</li>
</ul>

如果 <code>n</code> 是 快乐数 就返回 <code>true</code> ；不是，则返回 <code>false</code> 。

&nbsp;

示例 1：

<pre>
输入：n = 19
输出：true
解释：
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1
</pre>

示例 2：

<pre>
输入：n = 2
输出：false
</pre>

&nbsp;

提示：

<ul>
	<li><code>1 &lt;= n &lt;= 231 - 1</code></li>
</ul>