题解 | #二叉搜索树与双向链表 直接对双向链表进行处理#

/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

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

    }

}
*/
import java.util.*;
public class Solution {
    public TreeNode Convert(TreeNode pRootOfTree) {

        if (pRootOfTree == null) return pRootOfTree;
        LinkedList<TreeNode> ans = new LinkedList<>();
        process(pRootOfTree, ans);
        ans.addFirst(null);
        ans.addLast(null);
        TreeNode head = ans.peekFirst();
        for (int i = 1; i < ans.size() - 1; i++) {
            ans.get(i).left = ans.get(i - 1);
            ans.get(i).right = ans.get(i + 1);
        }
        return ans.get(1);
    }

    public static void process(TreeNode root, LinkedList<TreeNode> ans) {
        if (root == null) {
            return;
        }
        process(root.left, ans);
        ans.addLast(new TreeNode(root.val));
        process(root.right, ans);
    }
}