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2021-05-19

leet code

pre-order, in-order, post-order 모두 같은 패턴으로 풀 수 있었지만,

별로 메모리 효율적이지 못 했던 것 같아서 pre-oreder부터 다시 풀어봐야겠습니다.

특히 iterative한 방법으로 풀어봐야겠습니다.

930 - Binary Tree Postorder Traversal

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<int> postorderTraversal(TreeNode* root) {
        vector<int> rslt;
        if(!root) return rslt;
        return pt(root, rslt);
    }

    vector<int>& pt(TreeNode* root, vector<int>& retn)
    {
        // visit left
        if(root->left) pt(root->left, retn);
        // visit right
        if(root->right) pt(root->right, retn);
        // visit root
        retn.push_back(root->val);
        return retn;
    }
};