用c++实现二叉树的前序中序后序遍历

以下是使用C++实现二叉树的前序中序后序遍历的示例代码：

#include <iostream>
using namespace std;

// 定义二叉树结点
struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
};

// 构建二叉树
TreeNode* buildTree(int pre[], int in[], int preStart, int preEnd, int inStart, int inEnd) {
    if (preStart > preEnd || inStart > inEnd) {
        return nullptr;
    }

    int rootVal = pre[preStart];
    int rootIndex = 0;
    for (int i = inStart; i <= inEnd; i++) {
        if (in[i] == rootVal) {
            rootIndex = i;
            break;
        }
    }

    int leftLen = rootIndex - inStart;
    TreeNode* root = new TreeNode(rootVal);
    root->left = buildTree(pre, in, preStart + 1, preStart + leftLen, inStart, rootIndex - 1);
    root->right = buildTree(pre, in, preStart + leftLen + 1, preEnd, rootIndex + 1, inEnd);

    return root;
}

// 前序遍历
void preOrder(TreeNode* root) {
    if (root == nullptr) {
        return;
    }
    cout << root->val << " ";
    preOrder(root->left);
    preOrder(root->right);
}

// 中序遍历
void inOrder(TreeNode* root) {
    if (root == nullptr) {
        return;
    }
    inOrder(root->left);
    cout << root->val << " ";
    inOrder(root->right);
}

// 后序遍历
void postOrder(TreeNode* root) {
    if (root == nullptr) {
        return;
    }
    postOrder(root->left);
    postOrder(root->right);
    cout << root->val << " ";
}

int main() {
    int pre[] = {1, 2, 4, 5, 3, 6, 7};
    int in[] = {4, 2, 5, 1, 6, 3, 7};

    TreeNode* root = buildTree(pre, in, 0, 6, 0, 6);

    cout << "前序遍历结果：";
    preOrder(root);
    cout << endl;

    cout << "中序遍历结果：";
    inOrder(root);
    cout << endl;

    cout << "后序遍历结果：";
    postOrder(root);
    cout << endl;

    return 0;
}

在上面的代码中，我们首先定义了二叉树结点结构体`TreeNode`，然后实现了一个`buildTree`函数，该函数用于根据前序遍历数组和中序遍历数组构建二叉树。接着，我们分别实现了前序遍历、中序遍历和后序遍历的函数，最后在主函数中调用这些函数进行遍历。