Update Solution.c

Author: yanglbme

solution/0000-0099/0017.Letter Combinations of a Phone Number/Solution.c

@@ -1,27 +1,37 @@
-char* map[] = {"", "", "abc", "def", "ghi",
-    "jkl", "mno", "pqrs", "tuv", "wxyz"};
+char* d[] = {"abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
 
-void backtrack(char* d, int i, char* cur, char** res, int* sz) {
-    if (!d[i]) {
-        res[(*sz)++] = strdup(cur);
-        return;
+char** letterCombinations(char* digits, int* returnSize) {
+    if (!*digits) {
+        *returnSize = 0;
+        return NULL;
     }
-    for (char* p = map[d[i] - '0']; *p; p++) {
-        cur[i] = *p;
-        backtrack(d, i + 1, cur, res, sz);
+
+    int size = 1;
+    char** ans = (char**) malloc(sizeof(char*));
+    ans[0] = strdup("");
+
+    for (int x = 0; digits[x]; ++x) {
+        char* s = d[digits[x] - '2'];
+        int len = strlen(s);
+        char** t = (char**) malloc(sizeof(char*) * size * len);
+        int tSize = 0;
+
+        for (int i = 0; i < size; ++i) {
+            for (int j = 0; j < len; ++j) {
+                int oldLen = strlen(ans[i]);
+                char* tmp = (char*) malloc(oldLen + 2);
+                strcpy(tmp, ans[i]);
+                tmp[oldLen] = s[j];
+                tmp[oldLen + 1] = '\0';
+                t[tSize++] = tmp;
+            }
+            free(ans[i]);
+        }
+        free(ans);
+        ans = t;
+        size = tSize;
     }
-}
 
-char** letterCombinations(char* d, int* sz) {
-    *sz = 0;
-    if (!*d)
-        return NULL;
-    int max = 1, len = strlen(d);
-    for (int i = 0; i < len; i++)
-        max *= (d[i] == '7' || d[i] == '9') ? 4 : 3;
-    char **res = malloc(max * sizeof(char*)), *cur = malloc(len + 1);
-    cur[len] = '\0';
-    backtrack(d, 0, cur, res, sz);
-    free(cur);
-    return res;
+    *returnSize = size;
+    return ans;
 }