题目

二叉树及三种顺序的递归遍历

思路

代码

/**
 * @Author: ggdpzhk
 * @CreateTime: 2024-08-04
 *
 * 二叉树及三种顺序的递归遍历
 * LeetCode 144. 二叉树的前序遍历
 * LeetCode 94. 二叉树的中序遍历
 * LeetCode 145. 二叉树的后序遍历
 * LeetCode 102. 二叉树的层序遍历
 */
public class _017_Tree {

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

        System.out.println("先序遍历递归版");
        preOrder(head);
        System.out.println();

        System.out.println("中序遍历递归版");
        inOrder(head);
        System.out.println();

        System.out.println("后序遍历递归版");
        postOrder(head);
        System.out.println();
    }

    public static class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode(int x) {
            val = x;
        }
    }
    //先序打印所有节点 递归版
    public static void preOrder(TreeNode head) {
         if (head == null) {
             return;
         }
        System.out.print(head.val + " ");//先遍历我自己
        preOrder(head.left);//再遍历左子树
        preOrder(head.right);//再遍历右子树
    }

    //中序打印所有节点，递归版
    public static void inOrder(TreeNode head) {
        if (head == null) {
            return;
        }
        inOrder(head.left);
        System.out.print(head.val+" ");//左树结束，回到我，打印我
        inOrder(head.right);
    }

    //后序打印所有节点，递归版
    public static void postOrder(TreeNode head) {
        if(head == null){
            return;
        }
        postOrder(head.left);
        postOrder(head.right);
        System.out.print(head.val+" ");//左树右树遍历结束，回到我，打印我
    }
}

运行结果