Restore ip address

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

093_restore_ip_addresses/Makefile

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

093_restore_ip_addresses/ip_addr.c

@@ -0,0 +1,81 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+
+static bool valid(char *ip, int len)
+{
+    if (len > 1 && ip[0] == '0') {
+        return false;
+    }
+    if (len == 3) {
+        int n = (ip[0] - '0') * 100 + (ip[1] - '0') * 10 + (ip[2] - '0');
+        if (n > 255) {
+            return false;
+        }
+    }
+    return true;
+}
+
+#define WIDTH 4
+
+static void recursive(char *s, int start, char *stack, int num, char **results, int *count)
+{
+    int i, j;
+    if (num == 4) {
+        if (s[start] == '\0') {
+            results[*count] = malloc(3 * 4 + 3 + 1);
+            char *p = results[*count];
+            for (j = 0; j < num; j++) {
+                char *q = stack + j * WIDTH;
+                while ((*p++ = *q++) != '\0') {}
+                if (j != 3) {
+                    *(p - 1) = '.';
+                }
+            }
+            (*count)++;
+        }
+    } else {
+        char *p = stack + num * WIDTH;
+        char *q = p;
+        /* start + 3 indicates each ip number should not exceed size of 3 */
+        for (i = start; s[i] != '\0' && i < start + 3; i++) {
+            *q++ = s[i];
+            *q = '\0';
+            if (!valid(p, q - p)) {
+                return;
+            }
+            recursive(s, i + 1, stack, num + 1, results, count);
+            if (num + 1 < 4) {
+                memset(stack + (num + 1) * WIDTH, 0, WIDTH);
+            }
+        }
+    }
+}
+
+/**
+ ** Return an array of size *returnSize.
+ ** Note: The returned array must be malloced, assume caller calls free().
+ **/
+static char** restoreIpAddresses(char* s, int* returnSize) {
+    int count = 0;
+    char **results = malloc(100 * sizeof(char *));
+    char addr[16] = { '\0' };
+    recursive(s, 0, addr, 0, results, &count);
+    *returnSize = count;
+    return results;
+}
+
+int main(int argc, char **argv)
+{
+    if (argc != 2) {
+        fprintf(stderr, "Usage: ./test num\n");
+        exit(-1);
+    }
+
+    int i, count = 0;
+    char **list = restoreIpAddresses(argv[1], &count);
+    for (i = 0; i < count; i++) {
+        printf("%s\n", list[i]);
+    }
+}