c++建立一个二叉树用前序后序以及中序遍历法输出

好的，下面是一个基于前序、中序和后序遍历结果构建二叉树，并输出前序、中序和后序遍历结果的 C++ 代码示例：

#include <iostream>
#include <vector>
using namespace std;

// 定义二叉树节点结构体
struct TreeNode {
    char val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(char x) : val(x), left(NULL), right(NULL) {}
};

// 根据前序、中序和后序遍历结果构造二叉树
TreeNode* buildTree(vector<char>& preorder, vector<char>& inorder, vector<char>& postorder, int pre_start, int pre_end, int in_start, int in_end, int post_start, int post_end) {
    if (pre_start > pre_end || in_start > in_end || post_start > post_end) return NULL;
    TreeNode* root = new TreeNode(preorder[pre_start]);
    int index = 0;
    for (int i = in_start; i <= in_end; i++) {
        if (inorder[i] == root->val) {
            index = i;
            break;
        }
    }
    int left_len = index - in_start;
    root->left = buildTree(preorder, inorder, postorder, pre_start + 1, pre_start + left_len, in_start, index - 1, post_start, post_start + left_len - 1);
    root->right = buildTree(preorder, inorder, postorder, pre_start + left_len + 1, pre_end, index + 1, in_end, post_start + left_len, post_end - 1);
    return root;
}

// 输出前序遍历结果
void preorderTraversal(TreeNode* root) {
    if (root == NULL) return;
    cout << root->val << " ";
    preorderTraversal(root->left);
    preorderTraversal(root->right);
}

// 输出中序遍历结果
void inorderTraversal(TreeNode* root) {
    if (root == NULL) return;
    inorderTraversal(root->left);
    cout << root->val << " ";
    inorderTraversal(root->right);
}

// 输出后序遍历结果
void postorderTraversal(TreeNode* root) {
    if (root == NULL) return;
    postorderTraversal(root->left);
    postorderTraversal(root->right);
    cout << root->val << " ";
}

int main() {
    vector<char> preorder = {'A', 'B', 'D', 'E', 'C', 'F'};
    vector<char> inorder = {'D', 'B', 'E', 'A', 'F', 'C'};
    vector<char> postorder = {'D', 'E', 'B', 'F', 'C', 'A'};
    TreeNode* root = buildTree(preorder, inorder, postorder, 0, preorder.size() - 1, 0, inorder.size() - 1, 0, postorder.size() - 1);
    cout << "前序遍历结果为：";
    preorderTraversal(root);
    cout << endl;
    cout << "中序遍历结果为：";
    inorderTraversal(root);
    cout << endl;
    cout << "后序遍历结果为：";
    postorderTraversal(root);
    return 0;
}

输出结果为：

前序遍历结果为：A B D E C F 
中序遍历结果为：D B E A F C 
后序遍历结果为：D E B F C A 

分别为前序、中序和后序遍历结果。