题解 | 二叉搜索树与双向链表

import java.util.*;
/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public TreeNode Convert(TreeNode pRootOfTree) {

        List<TreeNode> list = new ArrayList<>();
        toConvert(pRootOfTree, list);
        if (list.isEmpty()) return null;
        TreeNode lastNode = list.get(0);
        for (int i = 1; i < list.size(); i++) {
            TreeNode currentNode = list.get(i);
            lastNode.right = currentNode;
            currentNode.left = lastNode;
            lastNode = currentNode;
        }
        return list.get(0);
    }


    static public void toConvert(TreeNode pRootOfTree, List<TreeNode> list) {
        if (pRootOfTree == null) {
            return;
        }
        if (pRootOfTree.left != null) {
            toConvert(pRootOfTree.left, list);
        }
        list.add(pRootOfTree);
        if (pRootOfTree.right != null) {
            toConvert(pRootOfTree.right, list);
        }
    }
}