145.binary-tree-postorder-traversal.cpp

/*
 * @lc app=leetcode id=145 lang=cpp
 *
 * [145] Binary Tree Postorder Traversal
 */

// @lc code=start
/**
 * 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) {
        stack<TreeNode*> s;
        vector<int> ans;
        if (!root) return ans;

        s.push(root);
        while(!s.empty()){
            TreeNode* cur = s.top();
            s.pop();       
            ans.push_back(cur->val);
            if (cur->left)
                s.push(cur->left);
            if (cur->right)
                s.push(cur->right);     
        }
        reverse(ans.begin(), ans.end());
        return ans;
    }
};
// @lc code=end