设二叉树中每个结点的元素均为一个字符，按先序遍历的顺序建立二叉链表，编写递归算法交换该二叉树的左右孩子。 用C语言实现

以下是C语言实现：

#include <stdio.h>
#include <stdlib.h>

struct TreeNode {
    char val;
    struct TreeNode *left;
    struct TreeNode *right;
};

void swapTree(struct TreeNode* root) {
    if (root == NULL) {
        return;
    }
    struct TreeNode* temp = root->left;
    root->left = root->right;
    root->right = temp;
    swapTree(root->left);
    swapTree(root->right);
}

struct TreeNode* createTree() {
    char c;
    scanf("%c", &c);
    if (c == '#') {
        return NULL;
    }
    struct TreeNode* root = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->val = c;
    root->left = createTree();
    root->right = createTree();
    return root;
}

void preOrder(struct TreeNode* root) {
    if (root == NULL) {
        return;
    }
    printf("%c ", root->val);
    preOrder(root->left);
    preOrder(root->right);
}

int main() {
    struct TreeNode* root = createTree();
    printf("Original Tree: ");
    preOrder(root);
    printf("\n");
    swapTree(root);
    printf("Swapped Tree: ");
    preOrder(root);
    printf("\n");
    return 0;
}

输入格式：以先序遍历方式输入二叉树，若结点为空则用 '#' 表示。

输出格式：输出交换左右孩子后的二叉树，以先序遍历方式输出。

例如，输入：AB#CD##E#F##

输出：Original Tree: A B C D E F

Swapped Tree: A C D B F E