Binary Tree Postorder Traversal

Desicription

Given a binary tree, return the postorder traversal of its nodes’ values.

Example:

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Input: [1,null,2,3]
1
\
2
/
3
Output: [3,2,1]

Follow up: Recursive solution is trivial, could you do it iteratively?

Solution

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/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
private:
void traversal(TreeNode* cur, vector<int>& vec) {
if(cur == NULL)
return ;
traversal(cur->left, vec);
traversal(cur->right, vec);
vec.push_back(cur->val);
}
public:
vector<int> postorderTraversal(TreeNode* root) {
vector<int> vec;
traversal(root, vec);
return vec;
}
};