114. Flatten Binary Tree to Linked List

题目114. Flatten Binary Tree to Linked List

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

1,利用先序遍历

思路:利用先序遍历的顺序,就是线性表的顺序
要特别注意一点,要将节点的左孩子置为空

public class Solution {
    public void flatten(TreeNode root) {
        if(root == null){
            return;
        }
        
        Stack stack = new Stack();
        stack.push(root);
        TreeNode tail = new TreeNode(1);
        TreeNode header = tail;
        while(!stack.empty()){
            TreeNode node = stack.pop();
            if(node.right != null){
                stack.push(node.right);
            }
            
            if(node.left != null){
                stack.push(node.left);
            }
            
            tail.right = node;
            tail = tail.right;
            //重要
            tail.left = null;
        }
        root = header.right;
    }
}