二刷202

Author: diguage

docs/0202-happy-number.adoc

@@ -1,32 +1,69 @@
 [#0202-happy-number]
-= 202. Happy Number
+= 202. 快乐数
 
-{leetcode}/problems/happy-number/[LeetCode - Happy Number^]
+https://leetcode.cn/problems/happy-number/[LeetCode - 202. 快乐数 ^]
 
-竟然可以使用"双指针"，类似判断链表中是否有环的思路！妙！
+编写一个算法来判断一个数 `n` 是不是快乐数。
 
+*「快乐数」* 定义为：
 
-Write an algorithm to determine if a number is "happy".
+* 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。
+* 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。
+* 如果这个过程 *结果为* 1，那么这个数就是快乐数。
 
-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.
+如果 `n` 是 _快乐数_ 就返回 `true` ；不是，则返回 `false` 。
 
-*Example: *
+*示例 1：*
 
-[subs="verbatim,quotes,macros"]
-----
-*Input:* 19
-*Output:* true
-*Explanation: 
-*1^2^ + 9^2^ = 82
-8^2^ + 2^2^ = 68
-6^2^ + 8^2^ = 100
-1^2^ + 0^2^ + 0^2^ = 1
-----
+....
+输入：n = 19
+输出：true
+解释：
+12 + 92 = 82
+82 + 22 = 68
+62 + 82 = 100
+12 + 02 + 02 = 1
+....
+
+*示例 2：*
+
+....
+输入：n = 2
+输出：false
+....
+
+
+*提示：*
+
+* `+1 <= n <= 2+`^`+31+`^`+-1+`
 
+== 思路分析
+
+竟然可以使用"双指针"，类似判断链表中是否有环的思路！妙！
+
+双指针的思路，来个图就一目了然了：
+
+image::images/0202-01.png[{image_attr}]
 
 [[src-0202]]
+[tabs]
+====
+一刷::
++
+--
 [{java_src_attr}]
 ----
 include::{sourcedir}/_0202_HappyNumber.java[tag=answer]
 ----
+--
+
+二刷::
++
+--
+[{java_src_attr}]
+----
+include::{sourcedir}/_0202_HappyNumber_2.java[tag=answer]
+----
+--
+====
 

docs/images/0202-01.png

@@ -50,6 +50,11 @@ endif::[]
 |{doc_base_url}/0141-linked-list-cycle.adoc[题解]
 |✅ 快慢指针
 
+|{counter:codes2503}
+|{leetcode_base_url}/happy-number/[202. 快乐数^]
+|{doc_base_url}/0202-happy-number.adoc[题解]
+|✅ 快慢指针
+
 |===
 
 截止目前，本轮练习一共完成 {codes2503} 道题。

logbook/202503.adoc

@@ -32,6 +32,9 @@ public class _0202_HappyNumber {
      * Memory Usage: 33.4 MB, less than 10.60% of Java online submissions for Happy Number.
      *
      * Copy from: https://leetcode.com/problems/happy-number/discuss/56917/My-solution-in-C(-O(1)-space-and-no-magic-math-property-involved-)[My solution in C( O(1) space and no magic math property involved ) - LeetCode Discuss]
+     *
+     * @author D瓜哥 · https://www.diguage.com
+     * @since 2020-01-10 21:40
      */
     public boolean isHappy(int n) {
         int slow = n;

src/main/java/com/diguage/algo/leetcode/_0202_HappyNumber.java

@@ -0,0 +1,34 @@
+package com.diguage.algo.leetcode;
+
+public class _0202_HappyNumber_2 {
+  // tag::answer[]
+
+/**
+ * @author D瓜哥 · https://www.diguage.com
+ * @since 2020-01-10 21:40
+ */
+public boolean isHappy(int n) {
+  int slow = n, fast = n;
+  do {
+    slow = squareSum(slow);
+    fast = squareSum(fast);
+    fast = squareSum(fast);
+    if (fast == 1) {
+      return true;
+    }
+  } while (slow != fast);
+
+  return false;
+}
+
+private int squareSum(int num) {
+  int sum = 0;
+  while (num > 0) {
+    int n = num % 10;
+    sum += n * n;
+    num /= 10;
+  }
+  return sum;
+}
+// end::answer[]
+}