Binary Tree Postorder Traversal Problem
Description
LeetCode Problem 145.
Given the root of abinary tree, return the postorder traversal of its nodes’ values.
Example 1:
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Input: root = [1,null,2,3]
Output: [3,2,1]
Example 2:
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Input: root = []
Output: []
Example 3:
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Input: root = [1]
Output: [1]
Example 4:
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Input: root = [1,2]
Output: [2,1]
Example 5:
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Input: root = [1,null,2]
Output: [2,1]
Constraints:
- The number of the nodes in the tree is in the range [0, 100].
- -100 <= Node.val <= 100
Sample C++ Code
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class Solution {
public:
vector<int> postorderTraversal(TreeNode* root) {
vector<int> postorder;
if (root == NULL)
return postorder;
stack<TreeNode*> s1, s2;
s1.push(root);
TreeNode* curr;
while(!s1.empty()) {
curr = s1.top();
s1.pop();
if (curr->left != NULL)
s1.push(curr->left);
if (curr->right != NULL)
s1.push(curr->right);
s2.push(curr);
}
while(!s2.empty()) {
curr = s2.top();
postorder.push_back(curr->val);
s2.pop();
}
return postorder;
}
};