二叉树非递归遍历实现完整代码

二叉树的非递归遍历可以使用栈来实现。以下是二叉树的非递归前序、中序和后序遍历的完整代码实现：

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

// 二叉树节点的定义
struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

// 非递归前序遍历
void preorderTraversal(TreeNode* root) {
    if (root == NULL) return;
    stack<TreeNode*> st;
    st.push(root);
    while (!st.empty()) {
        TreeNode* node = st.top();
        st.pop();
        cout << node->val << " ";
        if (node->right) st.push(node->right);
        if (node->left) st.push(node->left);
    }
}

// 非递归中序遍历
void inorderTraversal(TreeNode* root) {
    stack<TreeNode*> st;
    TreeNode* node = root;
    while (node != NULL || !st.empty()) {
        while (node != NULL) {
            st.push(node);
            node = node->left;
        }
        node = st.top();
        st.pop();
        cout << node->val << " ";
        node = node->right;
    }
}

// 非递归后序遍历
void postorderTraversal(TreeNode* root) {
    stack<TreeNode*> st;
    TreeNode* node = root;
    TreeNode* lastVisited = NULL;
    while (node != NULL || !st.empty()) {
        while (node != NULL) {
            st.push(node);
            node = node->left;
        }
        TreeNode* topNode = st.top();
        if (topNode->right == NULL || topNode->right == lastVisited) {
            cout << topNode->val << " ";
            st.pop();
            lastVisited = topNode;
        } else {
            node = topNode->right;
        }
    }
}

int main() {
    // 构造二叉树
    TreeNode* 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);

    // 非递归前序遍历
    cout << "Preorder traversal: ";
    preorderTraversal(root);
    cout << endl;

    // 非递归中序遍历
    cout << "Inorder traversal: ";
    inorderTraversal(root);
    cout << endl;

    // 非递归后序遍历
    cout << "Postorder traversal: ";
    postorderTraversal(root);
    cout << endl;

    return 0;
}