"Add Digits"

Author: lennylxx

README.md

@@ -31,7 +31,7 @@ The `☢` means that you need to have a LeetCode Premium Subscription.
 | 261 | [Graph Valid Tree]☢                                          |                    |
 | 260 | [Single Number III]                                          |                    |
 | 259 | [3Sum Smaller]☢                                              |                    |
-| 258 | [Add Digits]                                                 |                    |
+| 258 | [Add Digits]                                                 | [C](src/258.c)     |
 | 257 | [Binary Tree Paths]                                          |                    |
 | 256 | [Paint House]☢                                               |                    |
 | 255 | [Verify Preorder Sequence in Binary Search Tree]☢            |                    |

src/258.c

@@ -0,0 +1,31 @@
+#include <stdio.h>
+#include <assert.h>
+
+int addDigits0(int num) {
+    int ans = 0;
+    while (num > 0) {
+        ans += num % 10;
+        num /= 10;
+        if (ans >= 10) {
+            ans = ans / 10 + ans % 10;
+        }
+    }
+    return ans;
+}
+
+int addDigits(int num) {
+    return 1 + (num - 1) % 9;
+}
+
+int main() {
+
+    assert(addDigits(0) == 0);
+    assert(addDigits(1) == 1);
+    assert(addDigits(9) == 9);
+    assert(addDigits(38) == 2);
+    assert(addDigits(12345) == 6);
+
+    printf("all tests passed!\n");
+    
+    return 0;
+}