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[Leetcode] Binary Tree Inorder Traversal
Given a binary tree, return the inorder traversal of its nodes‘ values.
For example:
Given binary tree {1,#,2,3},
1 2 / 3
return [1,3,2].
Note: Recursive solution is trivial, could you do it iteratively?
Solution:
1. 非递归
1 /** 2 * Definition for binary tree 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */10 public class Solution {11 public List<Integer> inorderTraversal(TreeNode root) {12 List<Integer> result=new ArrayList<Integer>();13 if(root==null)14 return result;15 Stack<TreeNode> s=new Stack<TreeNode>();16 s.add(root);17 TreeNode p=root.left;18 while(!s.isEmpty()){19 while(p!=null){20 s.add(p);21 p=p.left;22 }23 TreeNode n=s.pop();24 result.add(n.val);25 p=n.right;26 if(p!=null){27 s.add(p);28 p=p.left;29 }30 }31 32 return result;33 }34 }
1 /** 2 * Definition for binary tree 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */10 public class Solution {11 12 ArrayList<Integer> result = new ArrayList<Integer>();13 14 public ArrayList<Integer> inorderTraversal(TreeNode root) {15 16 17 Stack<TreeNode> stack = new Stack<TreeNode>();18 while (root != null || !stack.empty()) {19 while (root != null) {20 stack.push(root);21 root = root.left;22 }23 if (stack.size() > 0) {24 root = stack.pop();25 result.add(root.val);26 root = root.right;27 }28 }29 30 return result;31 32 }33 }
2. 递归
1 /** 2 * Definition for binary tree 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */10 public class Solution {11 public List<Integer> inorderTraversal(TreeNode root) {12 List<Integer> result=new ArrayList<Integer>(); 13 myInorderTraversal(root,result); 14 return result;15 }16 17 private void myInorderTraversal(TreeNode root, List<Integer> result) {18 // TODO Auto-generated method stub19 if(root!=null){20 myInorderTraversal(root.left, result);21 result.add(root.val);22 myInorderTraversal(root.right, result);23 }24 }25 }
[Leetcode] Binary Tree Inorder Traversal
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