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) {
        if(pRootOfTree == null){
            return pRootOfTree;
        }
        Stack<TreeNode> stack = new Stack<>();
        TreeNode pre = null;
        while(pRootOfTree != null || !stack.isEmpty()){
            while(pRootOfTree != null){
                stack.push(pRootOfTree);
                pRootOfTree = pRootOfTree.left;
            }
            TreeNode curr = stack.pop();
            if(pre != null){
                pre.right = curr;
                curr.left = pre;
            }
            pre = curr;
            pRootOfTree = curr.right;
        }
        while(pre.left != null){
            pre = pre.left;
        }
        return pre;
    }
}

中序遍历，每次弹栈的时候修改当前节点和前面节点的指向关系，注意最后要返回最左边的节点