C++ 使用栈对二叉树进行后序遍历

#include <stack>
#include <iostream>
using namespace std;
// 假设二叉树节点定义如下
struct TreeNode {
    int value;
    TreeNode* left;
    TreeNode* right;

    TreeNode(int val) : value(val), left(nullptr), right(nullptr) {}
};

typedef TreeNode* BinTree;

void PostOrder(BinTree T) {
    if (T == nullptr) return;

    stack<BinTree> stack;
    BinTree current = T;
    BinTree lastVisited = nullptr;

    while (!stack.empty() || current != nullptr) {
        if (current != nullptr) {
            // 访问左子树
            stack.push(current);
            current = current->left;
        } else {
            // 检查是否可以访问右子树或回溯到父节点
            BinTree peekNode = stack.top();
            if (peekNode->right != nullptr && lastVisited != peekNode->right) {
                // 访问右子树
                current = peekNode->right;
            } else {
                // 访问节点
                cout << peekNode->value << " ";
                lastVisited = stack.top();
                stack.pop();
            }
        }
    }
}

// 示例：如何使用 PostOrder 函数
int main() {
    // 构建一个简单的二叉树
    //       1
    //      / \
    //     2   3
    //    / \
    //   4   5
    BinTree root = new TreeNode(1);
    root->left = new TreeNode(2);
    root->right = new TreeNode(3);
    root->left->left = new TreeNode(4);
    root->left->right = new TreeNode(5);

    PostOrder(root); // 输出: 4 5 2 3 1

    return 0;
}