refactor: Replace vector with array in C code (#894)

* Re-implement merge sort function.

* Replace vector with array for C.

* fix

codes/c/chapter_backtracking/preorder_traversal_i_compact.c

@@ -6,22 +6,20 @@
 
 #include "../utils/common.h"
 
-vector *res;
+// 假设结果长度不超过 100
+#define MAX_SIZE 100
 
-// 打印向量中的元素
-void printFunc(vector *v, void *p) {
-    TreeNode *node = p;
-    printf("%d ", node->val);
-}
+TreeNode *res[MAX_SIZE];
+int resSize = 0;
 
 /* 前序遍历：例题一 */
-void preOrder(TreeNode *root) {
+static void preOrder(TreeNode *root) {
     if (root == NULL) {
         return;
     }
     if (root->val == 7) {
         // 记录解
-        vectorPushback(res, root, sizeof(int));
+        res[resSize++] = root;
     }
     preOrder(root->left);
     preOrder(root->right);
@@ -30,15 +28,21 @@ void preOrder(TreeNode *root) {
 /* Driver Code */
 int main() {
     int arr[] = {1, 7, 3, 4, 5, 6, 7};
-    res = newVector();
-    TreeNode *root = arrToTree(arr, sizeof(arr) / sizeof(arr[0]));
-    printf("\n初始化二叉树\r\n");
+    TreeNode *root = arrayToTree(arr, sizeof(arr) / sizeof(arr[0]));
+    printf("\n初始化二叉树\n");
     printTree(root);
 
     // 前序遍历
     preOrder(root);
 
-    printf("\n输出所有值为 7 的节点\r\n");
-    printVector(res, printFunc);
-    delVector(res);
-}
+    printf("\n输出所有值为 7 的节点\n");
+    int vals[resSize];
+    for (int i = 0; i < resSize; i++) {
+        vals[i] = res[i]->val;
+    }
+    printArray(vals, resSize);
+
+    // 释放内存
+    freeMemoryTree(root);
+    return 0;
+}