LeetCode—114. Flatten Binary Tree to Linked List

LeetCode—114. Flatten Binary Tree to Linked List

题目

https://leetcode.com/problems/flatten-binary-tree-to-linked-list/description/

思路及方法

前序遍历二叉树，存到列表里，在建立新书。

代码

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public void flatten(TreeNode root) {
        List<TreeNode> list = new ArrayList<>();
        if(root==null) return;
        preOrder(list, root);
        int i=0;
        for(i=0; i<list.size()-1; i++){
            list.get(i).left = null;
            list.get(i).right = list.get(i+1);
        }
        list.get(i).left = null;
        list.get(i).right = null;
    }
    public void preOrder(List list, TreeNode node){
        if(node==null) return;
        list.add(node);
        if(node.left!=null) preOrder(list, node.left);
        if(node.right!=null) preOrder(list, node.right);
    }
}