LeetCode 38 Flatten Binary Tree to Linked List

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Given a binary tree, flatten it to a linked list in-place.

For example,

Given

    1   / \  2   5 / \   \3   4   6

The flattened tree should look like:

1 \  2   \    3     \      4       \        5         \          6

分析：

看见二叉树，首先想到递归，那么就是把左子树flattern接在root孩子，把右子树flattern接在左子树链的后面。

需要注意的是，左孩子指针要变成null.

/** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public void flatten(TreeNode root) {        if(root==null) return;        toLink(root);    }        public TreeNode toLink(TreeNode node){        if(node.left==null && node.right==null)            return node;        TreeNode rHead = null;        if(node.right != null){            rHead = toLink(node.right);            rHead.left = null;        }        TreeNode p = node;        if(node.left != null){            TreeNode lHead = toLink(node.left);            node.right = lHead;            node.left = null;            lHead.left = null;            while(p.right != null)                p = p.right;        }        p.right = rHead;        return node;    }}

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