題目描述

輸入一棵二叉搜尋樹，將該二叉搜尋樹轉換成一個排序的雙向連結串列。要求不能建立任何新的結點，只能調整樹中結點指標的指向

題目連結：https://www.nowcoder.com/practice/947f6eb80d944a84850b0538bf0ec3a5

解題思路

解法1：迭代（非遞迴）思路，模擬中序遍歷，記錄上一個遍歷的節點，同當前節點進行雙向指向
解法2：遞迴法

/**
 * 解法1：迭代（非遞迴）法
 */
import java.util.Stack;

public class Solution {
    public TreeNode Convert
 
(TreeNode pRootOfTree) {
        if (pRootOfTree == null) return null;
        
        Stack<TreeNode> stack = new Stack<>();
        TreeNode root = null;
        TreeNode p = pRootOfTree;
        TreeNode pre = null;
        boolean isFirst = true;
        
        while (p != null ||
 
 !stack.isEmpty()) {
            while (p != null) {
                stack.push(p);
                p = p.left;
            }
            p = stack.pop();
            if (isFirst) {
                root = p;
                pre = p;
                isFirst = false;
            } else {
                pre.
 
right = p;
                p.left = pre;
                pre = p;
            }
            p = p.right;
        }
        return root;
    }
}