解题思路

递归

迭代

代码

Python

递归

迭代

C++

递归

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class Solution {
public:
    vector<int> postorderTraversal(TreeNode* root) {
        vector<int> result;
        dfs(root, result);
        return result;
    }
    void dfs(TreeNode* node, vector<int> &result) {
        if (node == NULL) return;
        dfs(node->left, result);
        dfs(node->right, result);
        result.push_back(node->val);
    }
};

迭代

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class Solution {
public:
    vector<int> postorderTraversal(TreeNode* root) {
        vector<int> result;
        stack<TreeNode*> st;
        if (root != NULL) st.push(root);
        while (!st.empty()) {
            TreeNode* node = st.top();
            if (node != NULL) {
                st.pop();
                st.push(node);
                st.push(NULL);
                if (node->right) st.push(node->right);
                if (node->left) st.push(node->left);
            } else {
                st.pop();
                node = st.top();
                st.pop();
                result.push_back(node->val);
            }
        }
        return result;
    }
};