add problem 17 and test function

Author: supercoderhawk

C/1-50/17-Letter-Combinations-of-a-Phone-Number.c

@@ -0,0 +1,59 @@
+/*
+ * Given a digit string, return all possible letter combinations that the number could represent.
+
+ * Created by supercoderx on 2017/8/9.
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+char **letterCombinations(char *digits, int *returnSize) {
+    char *map[] = {"0", "1", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
+    int mapLen[] = {1, 1, 3, 3, 3, 3, 3, 4, 3, 4};
+    int len = 0, count = 0, id = 0;
+    char *tmp = digits, **result = NULL;
+
+    while (*tmp != '\0') {
+        len++;
+        tmp++;
+    }
+    (*returnSize) = 0;
+
+    for (int i = 0; i < len; i++) {
+        id = digits[i] - 0x30;
+        count = mapLen[id];
+        if (i == 0) {
+            result = malloc(sizeof(char *) * count);
+            for (int j = 0; j < count; j++) {
+                result[j] = malloc(sizeof(char) * (len + 1));
+                result[j][0] = map[id][j];
+                result[j][len] = '\0';
+            }
+            *returnSize = count;
+        } else {
+            result = realloc(result, sizeof(char *) * (*returnSize) * count);
+            for (int j = 0; j < count; j++) {
+
+                for (int k = 0; k < *returnSize; k++) {
+                    if (j > 0) {
+                        result[k + j * (*returnSize)] = malloc(sizeof(char) * (len + 1));
+                        result[k + j * (*returnSize)][len] = '\0';
+                        strncpy(result[k + j * (*returnSize)], result[k], i);
+                    }
+                    result[k + j * (*returnSize)][i] = map[id][j];
+                }
+            }
+            (*returnSize) *= count;
+        }
+    }
+    return result;
+}
+
+void testLetterCombinations() {
+    char str[] = "23";
+    int count = 0;
+    char **result = letterCombinations(str, &count);
+    for (int i = 0; i < count; i++) {
+        printf("%s,", result[i]);
+    }
+}