Merge pull request neetcode-gh#2198 from seinlin/535

Add 0535-encode-and-decode-tinyurl.c

c/0535-encode-and-decode-tinyurl.c

@@ -0,0 +1,55 @@
+// Represent an element in a hash table.
+typedef struct Hash {
+    char* key;
+    char* value;
+    UT_hash_handle hh;
+} Hash;
+
+Hash *root = NULL;
+
+char *UrlToKey(char *url) {
+    char *key = NULL;
+    unsigned int hash = 1853;
+    int i = 0;
+
+    while (i < strlen(url)) {
+        hash = ((hash << 5) + hash) + url[i];
+        i++;
+    }
+
+    key = (char*)calloc(32, 1);
+    snprintf(key, 32, "http://tinyurl.com/%X", hash);
+    return key;
+}
+
+/** Encodes a URL to a shortened URL. */
+char* encode(char* longUrl) {
+    Hash *entry = NULL;
+    char *key = NULL;
+    key = UrlToKey(longUrl);
+    HASH_FIND_STR(root, key, entry);
+    if (!entry) {
+        entry = malloc(sizeof(Hash));
+        entry->key = key;
+        entry->value = longUrl;
+        HASH_ADD_KEYPTR(hh, root, key, strlen(key), entry);
+    } else {
+        free(key);
+    }
+    return entry->key;
+}
+
+/** Decodes a shortened URL to its original URL. */
+char* decode(char* shortUrl) {
+    Hash *entry = NULL;
+    HASH_FIND_STR(root, shortUrl, entry);
+    if (entry) {
+        return entry->value;
+    }
+    return NULL;
+}
+
+// Your functions will be called as such:
+// char* s = encode(s);
+// decode(s);
+