树的前、中、后序遍历

满二叉树：

public class BinaryTree {
    private int[] arr;

    public BinaryTree(int[] arr) {
        this.arr = arr;
    }

    public void preOrder(int index) {
        if (arr == null || arr.length == 0) {
            System.out.println("数组为空");
        }
        System.out.println(arr[index]);
        if ((index * 2 + 1) < arr.length) {
            preOrder(index * 2 + 1);
        }
        if ((index * 2 + 2) < arr.length) {
            preOrder(index * 2 + 2);
        }
    }

    public void midOrder(int index) {
        if (arr == null || arr.length == 0) {
            System.out.println("数组为空");
        }
        if ((index * 2 + 1) < arr.length) {
            midOrder(index * 2 + 1);
        }
        System.out.println(arr[index]);
        if ((index * 2 + 2) < arr.length) {
            midOrder(index * 2 + 2);
        }
    }

    public void afterOrder(int index) {
        if (arr == null || arr.length == 0) {
            System.out.println("数组为空");
        }
        if ((index * 2 + 1) < arr.length) {
            afterOrder(index * 2 + 1);
        }
        if ((index * 2 + 2) < arr.length) {
            afterOrder(index * 2 + 2);
        }
        System.out.println(arr[index]);
    }
}

 public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5, 6, 7};
        BinaryTree binaryTree = new BinaryTree(arr);
        System.out.println("前序遍历：");
        binaryTree.preOrder(0);
        System.out.println("中序遍历：");
        binaryTree.midOrder(0);
        System.out.println("后序遍历：");
        binaryTree.afterOrder(0);
    }

输出结果：

前序遍历：
1
2
4
5
3
6
7
中序遍历：
4
2
5
1
6
3
7
后序遍历：
4
5
2
6
7
3
1

Process finished with exit code 0