LeetCode: Binary Tree Postorder Traversal

跟inorder差不多

 1 /**

 2  * Definition for binary tree

 3  * struct TreeNode {

 4  *     int val;

 5  *     TreeNode *left;

 6  *     TreeNode *right;

 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 8  * };

 9  */

10 class Solution {

11 public:

12     vector<int> postorderTraversal(TreeNode *root) {

13         vector<int> res;

14         stack<TreeNode *> S;

15         if (!root) return res;

16         S.push(root);

17         while (!S.empty()) {

18             TreeNode *top = S.top();

19             if (!top->left && !top->right) {

20                 res.push_back(top->val);

21                 S.pop();

22             }

23             else {

24                 if (top->right) {

25                     S.push(top->right);

26                     top->right = NULL;

27                 }

28                 if (top->left) {

29                     S.push(top->left);

30                     top->left = NULL;

31                 }

32             }

33         }

34         return res;

35     }

36 };

 C#

 1 /**

 2  * Definition for a binary tree node.

 3  * public class TreeNode {

 4  *     public int val;

 5  *     public TreeNode left;

 6  *     public TreeNode right;

 7  *     public TreeNode(int x) { val = x; }

 8  * }

 9  */

10 public class Solution {

11     public List<int> PostorderTraversal(TreeNode root) {

12         List<int> ans = new List<int>();

13         Stack<TreeNode> S = new Stack<TreeNode>();

14         if (root == null) return ans;

15         S.Push(root);

16         while (S.Count > 0) {

17             TreeNode peek = S.Peek();

18             if (peek.left == null && peek.right == null) {

19                 ans.Add(peek.val);

20                 S.Pop();

21             }

22             else {

23                 if (peek.right != null) {

24                     S.Push(peek.right);

25                     peek.right = null;

26                 }

27                 if (peek.left != null) {

28                     S.Push(peek.left);

29                     peek.left = null;

30                 }

31             }

32         }

33         return ans;

34     }

35 }

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