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_iii_template.c

@@ -6,96 +6,87 @@
 
 #include "../utils/common.h"
 
+// 假设路径和结果长度不超过 100
+#define MAX_SIZE 100
+#define MAX_RES_SIZE 100
+
+TreeNode *path[MAX_SIZE];
+TreeNode *res[MAX_RES_SIZE][MAX_SIZE];
+int pathSize = 0, resSize = 0;
+
 /* 判断当前状态是否为解 */
-bool isSolution(vector *state) {
-    return state->size != 0 && ((TreeNode *)(state->data[state->size - 1]))->val == 7;
+bool isSolution(void) {
+    return pathSize > 0 && path[pathSize - 1]->val == 7;
 }
 
 /* 记录解 */
-void recordSolution(vector *state, vector *res) {
-    vector *newPath = newVector();
-    for (int i = 0; i < state->size; i++) {
-        vectorPushback(newPath, state->data[i], sizeof(int));
+void recordSolution(void) {
+    for (int i = 0; i < pathSize; i++) {
+        res[resSize][i] = path[i];
     }
-    vectorPushback(res, newPath, sizeof(vector));
+    resSize++;
 }
 
 /* 判断在当前状态下，该选择是否合法 */
-bool isValid(vector *state, TreeNode *choice) {
+bool isValid(TreeNode *choice) {
     return choice != NULL && choice->val != 3;
 }
 
 /* 更新状态 */
-void makeChoice(vector *state, TreeNode *choice) {
-    vectorPushback(state, choice, sizeof(TreeNode));
+void makeChoice(TreeNode *choice) {
+    path[pathSize++] = choice;
 }
 
 /* 恢复状态 */
-void undoChoice(vector *state, TreeNode *choice) {
-    vectorPopback(state);
+void undoChoice(void) {
+    pathSize--;
 }
 
 /* 回溯算法：例题三 */
-void backtrack(vector *state, vector *choices, vector *res) {
+void backtrack(TreeNode *choices[2]) {
     // 检查是否为解
-    if (isSolution(state)) {
+    if (isSolution()) {
         // 记录解
-        recordSolution(state, res);
-        return;
+        recordSolution();
     }
     // 遍历所有选择
-    for (int i = 0; i < choices->size; i++) {
-        TreeNode *choice = choices->data[i];
+    for (int i = 0; i < 2; i++) {
+        TreeNode *choice = choices[i];
         // 剪枝：检查选择是否合法
-        if (isValid(state, choice)) {
+        if (isValid(choice)) {
             // 尝试：做出选择，更新状态
-            makeChoice(state, choice);
+            makeChoice(choice);
             // 进行下一轮选择
-            vector *nextChoices = newVector();
-            vectorPushback(nextChoices, choice->left, sizeof(TreeNode));
-            vectorPushback(nextChoices, choice->right, sizeof(TreeNode));
-            backtrack(state, nextChoices, res);
+            TreeNode *nextChoices[2] = {choice->left, choice->right};
+            backtrack(nextChoices);
             // 回退：撤销选择，恢复到之前的状态
-            undoChoice(state, choice);
+            undoChoice();
         }
     }
 }
 
-// 打印向量中的元素
-void printFunc(vector *v, void *p) {
-    TreeNode *node = p;
-    printf("%d ", node->val);
-}
-
 /* Driver Code */
 int main() {
     int arr[] = {1, 7, 3, 4, 5, 6, 7};
-    int n = sizeof(arr) / sizeof(arr[0]);
-    TreeNode *root = arrToTree(arr, n);
-    printf("\r\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);
 
     // 回溯算法
-    vector *state = newVector();
-    vector *choices = newVector();
-    vector *res = newVector();
-    vectorPushback(choices, root, sizeof(TreeNode));
-    backtrack(state, choices, res);
+    TreeNode *choices[2] = {root, NULL};
+    backtrack(choices);
 
-    printf("输出所有根节点到节点 7 的路径，要求路径中不包含值为 3 的节点:\n");
-    for (int i = 0; i < res->size; i++) {
-        vector *path = res->data[i];
-        vector *vals = newVector();
-        for (int j = 0; j < path->size; j++) {
-            TreeNode *node = path->data[j];
-            vectorPushback(vals, &node->val, sizeof(int));
+    printf("\n输出所有根节点到节点 7 的路径，要求路径中不包含值为 3 的节点\n");
+    for (int i = 0; i < resSize; ++i) {
+        int vals[MAX_SIZE];
+        int size = 0;
+        for (int j = 0; res[i][j] != NULL; ++j) {
+            vals[size++] = res[i][j]->val;
         }
-        printVector(vals, printFunc);
+        printArray(vals, size);
     }
 
     // 释放内存
-    delVector(state);
-    delVector(choices);
-    delVector(res);
+    freeMemoryTree(root);
     return 0;
 }