114. Flatten Binary Tree to Linked List - Medium

发布时间：2020-12-14 05:17:34 所属栏目：大数据来源：网络整理

导读：Given a binary tree,flatten it to a linked list in-place. For example,given the following tree: 1 / 2 5 / 3 4 6 The flattened tree should look like: 1 2 3 4 5 6 ? 每个节点的右节点都是preorder traverse的下一个节点 -?应该先?反preorder遍历

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

For example,given the following tree:

    1
   /   2   5
 /    3   4   6

The flattened tree should look like:

每个节点的右节点都是preorder traverse的下一个节点 ->?应该先?反preorder遍历 (即node.right->node.left->node) 到最后，从最后开始relink

time: O(n),space: O(height)

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    TreeNode prev = null;
    
    public void flatten(TreeNode root) {
        if(root == null) {
            return;
        }
        
        flatten(root.right);
        flatten(root.left);
        
        root.right = prev;
        root.left = null;
        prev = root;
    }
}

（编辑：李大同）

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