Count and say

Signed-off-by: Leo Ma <[email protected]>

038_count_and_say/Makefile

@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test count_and_say.c

038_count_and_say/count_and_say.c

@@ -0,0 +1,75 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static void parse(char *input, char *output)
+{
+    char *p = input;
+    char *q = output;
+
+    while (*p != '\0') {
+        int count = 1;
+        while (p[0] == p[1]) {
+            count++;
+            p++;
+        }
+
+        /* reverse number */
+        int n = 0;
+        while (count > 0) {
+            n += count % 10;
+            count /= 10;
+        }
+
+        /* parse count */
+        while (n > 0) {
+            *q++ = (n % 10) + '0';
+            n /= 10;
+        }
+
+        *q++ = p[0];
+        p++;
+    }
+
+    *q = '\0';
+}
+
+static char *countAndSay(int n)
+{
+    if (n < 1) {
+        return NULL;
+    }
+
+    char *result;
+    char *prev = malloc(10000);
+    char *next = malloc(10000);
+    strcpy(prev, "1");
+
+    if (n == 1) {
+        return prev;
+    }
+
+    int i;
+    for (i = 2; i <= n; i++) {
+        if (i & 0x1) {
+           parse(next, prev);
+           result = prev;
+        } else {
+           parse(prev, next);
+           result = next;
+        }
+    }
+
+    return result;
+}
+
+int main(int argc, char **argv)
+{
+    if (argc != 2) {
+        fprintf(stderr, "Usage: ./test n\n");
+        exit(-1);
+    }
+
+    printf("%s\n", countAndSay(atoi(argv[1])));
+    return 0;
+}