二叉树的非递归遍历完整代码

二叉树的非递归遍历可以使用栈来实现。以下是三种遍历方式的完整代码：

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);
    }
}

中序遍历：

void inorderTraversal(TreeNode* root) {
    if (root == NULL) return;
    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;
    }
}

后序遍历：

void postorderTraversal(TreeNode* root) {
    if (root == NULL) return;
    stack<TreeNode*> st1, st2;
    st1.push(root);
    while (!st1.empty()) {
        TreeNode* node = st1.top();
        st1.pop();
        st2.push(node);
        if (node->left) st1.push(node->left);
        if (node->right) st1.push(node->right);
    }
    while (!st2.empty()) {
        TreeNode* node = st2.top();
        st2.pop();
        cout << node->val << " ";
    }
}