二叉樹中序遍歷
給出一棵二叉樹,返回其中序遍歷
給出二叉樹 {1,#,2,3}
,
1 \ 2 / 3
返回 [1,3,2]
.
二叉樹中序遍歷:左子樹->根節點->右子樹。下圖二叉樹中序遍歷結果爲:debgfac。
通過遞歸方式實現二叉樹中序遍歷的代碼如下:
/**
* Definition of TreeNode:
* public class TreeNode {
* public int val;
* public TreeNode left, right;
* public TreeNode(int val) {
* this.val = val;
* this.left = this.right = null;
* }
* }
*/
public class Solution {
/**
* @param root: The root of binary tree.
* @return: Inorder in ArrayList which contains node values.
*/
ArrayList<Integer> list = new ArrayList<Integer>();
public ArrayList<Integer> inorderTraversal(TreeNode root) {
// write your code here
inorder(root);
return list;
}
private void inorder(TreeNode root){
if(root == null) return;
inorder(root.left);
list.add(root.val);
inorder(root.right);
}
}
通過非遞歸方式實現二叉樹中序遍歷的代碼如下:
/**
* Definition of TreeNode:
* public class TreeNode {
* public int val;
* public TreeNode left, right;
* public TreeNode(int val) {
* this.val = val;
* this.left = this.right = null;
* }
* }
*/
public class Solution {
/**
* @param root: The root of binary tree.
* @return: Inorder in ArrayList which contains node values.
*/
public ArrayList<Integer> inorderTraversal(TreeNode root) {
// write your code here
Stack<TreeNode> stack = new Stack<TreeNode>();
ArrayList<Integer> list = new ArrayList<Integer>();
while(root!=null||stack.size()>0){
while(root!=null){
stack.push(root);
root = root.left;
}
if(stack.size()>0){
root = stack.pop();
list.add(root.val);
root = root.right;
}
}
return list;
}
}