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94. Binary Tree Inorder Traversal

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

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

   1         2    /   3

 

return [1,3,2].

思路:中序遍历。

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

 

94. Binary Tree Inorder Traversal