58-二叉树的后序遍历

递归

算法实现

class Solution {
public:

    void postorder(TreeNode * root, vector<int> & res) {
        if(root != nullptr) {
            postorder(root->left, res);
            postorder(root->right, res);
            res.push_back(root->val);
        }

    }
    vector<int> postorderTraversal(TreeNode* root) {
        vector<int> res;
        postorder(root,res);
        return res;
    }
};

颜色标记法

算法实现

class Solution {
public:

    vector<int> postorderTraversal(TreeNode* root) {
        vector<int> res;
        stack<pair<TreeNode *, int>> s;
        s.push({root, 0});
        while (!s.empty()) {
            pair<TreeNode *, int> node = s.top();
            s.pop();
            if(node.first == nullptr) {
                continue;
            }
            if(!node.second) {
                s.push({node.first, 1});
                s.push({node.first->right, 0});
                s.push({node.first->left, 0});
            } else {
                res.push_back(node.first->val);
            }
        }
        return res;
    }
};