添加 0202快乐数 C 版本

problems/0202.快乐数.md

@@ -423,29 +423,61 @@ impl Solution {
 ### C:
 
 ```C
-typedef struct HashNodeTag {
-    int key;   /* num  */
-    struct HashNodeTag *next;
-}HashNode;
-
-/* Calcualte the hash key */
-static inline int hash(int key, int size) {
-    int index = key % size;
-    return (index > 0) ? (index) : (-index);
-}
-
-/* Calculate the sum of the squares of its digits*/
-static inline int calcSquareSum(int num) {
-    unsigned int sum = 0;
-    while(num > 0) {
-        sum += (num % 10) * (num % 10);
-        num = num/10; 
+int get_sum(int n) {
+    int sum = 0;
+    div_t n_div = { .quot = n };
+    while (n_div.quot != 0) {
+        n_div = div(n_div.quot, 10);
+        sum += n_div.rem * n_div.rem;
     }
     return sum;
 }
 
+// (版本1)使用数组
+bool isHappy(int n) {
+    // sum = a1^2 + a2^2 + ... ak^2
+    // first round:
+    // 1 <= k <= 10
+    // 1 <= sum <= 1 + 81 * 9 = 730
+    // second round:
+    // 1 <= k <= 3
+    // 1 <= sum <= 36 + 81 * 2 = 198
+    // third round:
+    // 1 <= sum <= 81 * 2 = 162
+    // fourth round:
+    // 1 <= sum <= 81 * 2 = 162
 
-Scala:
+    uint8_t visited[163] = { 0 };
+    int sum = get_sum(get_sum(n));
+    int next_n = sum;
+
+    while (next_n != 1) {
+        sum = get_sum(next_n);
+
+        if (visited[sum]) return false;
+
+        visited[sum] = 1;
+        next_n = sum;
+    };
+
+    return true;
+}
+
+// (版本2)使用快慢指针
+bool isHappy(int n) {
+    int slow = n;
+    int fast = n;
+
+    do {
+        slow = get_sum(slow);
+        fast = get_sum(get_sum(fast));
+    } while (slow != fast);
+
+    return (fast == 1);
+}
+```
+
+### Scala:
 ```scala
 object Solution {
   // 引入mutable