递归序：给定先序、中序，获取该树-优快云博客

本文链接：https://blog.youkuaiyun.com/junzhao09/article/details/129673042

这段代码定义了一个Node类，用于创建二叉树结构。fun方法进行先序遍历，f方法根据预序和中序遍历数组重建二叉树。在main方法中，首先手动构建了一棵树并进行先序遍历，然后使用给定的预序和中序遍历数组重建并打印一棵树。

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public class Code {
	public static class Node {
        public int value;
        public Node left;
        public Node right;

        public Node(int v) {
            value = v;
        }
    }

    public static void fun(Node node) {
        if (Objects.isNull(node)) {
            return;
        }


        fun(node.left);
        fun(node.right);
        System.out.print(node.value + " ");
    }


    public static Node f(int[] pre, int L1, int R1, int[] in, int L2, int R2) {
        if (L1 > R1) {
            return null;
        }

        Node head = new Node(pre[L1]);
        if (L1 == R1) {
            return head;
        }

        int middle = L2;
        while (in[middle] != pre[L1]) {
            middle++;
        }

        head.left = f(
                pre,
                L1 + 1,
                L1 + middle - L2,
                in,
                L2,
                middle - 1
                );

        head.right = f(
                pre,
                L1 + middle - L2 + 1,
                R1,
                in,
                middle + 1,
                R2
        );
        return head;
    }

    public static void main(String[] args) {
        Node node = new Node(1);
        node.left = new Node(2);
        node.left.left = new Node(4);
        node.left.right = new Node(5);
        node.right = new Node(3);
        node.right.left = new Node(6);
        node.right.right = new Node(7);

        fun(node);
        System.out.println("===================================");

        int[] pre = {1, 2, 4, 5, 3, 6, 7};
        int[] in =  {4, 2, 5, 1, 6, 3, 7};
        Node treeNode = f(pre, 0, pre.length - 1 , in, 0, in.length - 1);
        fun(treeNode);

    }
}