【LeetCode】剑指 Offer 36. 二叉搜索树与双向链表

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• 【LeetCode】剑指 Offer 36. 二叉搜索树与双向链表

package offer;

//定义节点
class Node{
    int value;
    Node left;
    Node right;

    public Node(int value){
        this.value = value;
    }

    public Node(int value, Node left, Node right){
        this.value = value;
        this.left = left;
        this.right = right;
    }

    @Override
    public String toString() {
        return "Node{" +
                "value=" + value +
                '}';
    }
}


public class Solution36 {
    public static void main(String[] args) {
        Node node1 = new Node(4);
        Node node2 = new Node(2);
        Node node3 = new Node(5);
        Node node4 = new Node(1);
        Node node5 = new Node(3);
        node1.left = node2;
        node1.right = node3;
        node2.left = node4;
        node2.right = node5;
        Solution36 solution = new Solution36();
        System.out.println(solution.method(node1));
    }

    Node pre;
    Node head;

    private Node method(Node root){
        if(root == null) return null;
        dfs(root);
        head.left = pre;
        pre.right = head;
        return head;
    }

    private void dfs(Node cur){
        if(cur == null) return;
        dfs(cur.left);
        if(pre != null) pre.right = cur;
        else head = cur;
        cur.left = pre;
        pre = cur;
        dfs(cur.right);
    }
}

//时间复杂度为 O(n)
//空间复杂度为 O(n)