中序遍历二叉树 Binary Tree Inorder Traversal

最新推荐文章于 2025-08-08 22:01:10 发布

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原文链接：https://my.oschina.net/liyurong/blog/1539264

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#数据结构与算法

为什么80%的码农都做不了架构师？>>>

问题：

Given a binary tree, return the inorder traversal of its nodes' values.

For example:
Given binary tree [1,null,2,3],

return [1,3,2].

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

解决：

① 递归中序遍历。

/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {//1ms
public List<Integer> inorderTraversal(TreeNode root) {
List<Integer> res = new ArrayList<>();
inorder(root,res);
return res;
}
public void inorder(TreeNode root,List<Integer> res){
if(root == null) return;
inorder(root.left,res);
res.add(root.val);
inorder(root.right,res);
}
}

② 非递归方法。

class Solution {//2ms
public List<Integer> inorderTraversal(TreeNode root) {
List<Integer> res = new ArrayList<>();
if(root == null) return res;
Stack<TreeNode> stack = new Stack<>();
TreeNode cur = root;
while(! stack.isEmpty() || cur != null){
while(cur != null){
stack.push(cur);
cur = cur.left;
}
cur = stack.pop();
res.add(cur.val);
cur = cur.right;
}
return res;
}
}