Leetcode#144Binary Tree Preorder Traversal

Binary Tree Preorder Traversal

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Question Solution

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

For example:
Given binary tree {1,#,2,3},

   1
         2
    /
   3

return [1,2,3].

分析：先序遍历树中的节点，采用递归的方法

public class Solution {

List<Integer> x=new ArrayList<Integer>();

void preTra(TreeNode r) {

if(r!=null)

{

x.add(r.val);

preTra(r.left);

preTra(r.right);

}

}

public List<Integer> preorderTraversal(TreeNode root) {

preTra(root);

return x;

}

}