根据层序和中序构建二叉树

小红书的笔试题

题目记不全了，反正就是提供层序序列和中序序列。输出是前序序列和后序序列，以及从左到右的输出叶子节点。

 

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {

	public static Map<Integer,Integer> map;
    public static Node build(int[] c, int[] z){
        Node root = create(c,z,0,c.length);
        return root;
    }
    public static Node create(int[] c,int[] z,int s,int e){

        int minI = c.length;
//        System.out.println(s+" : "+e);
        int curr = s;
        for (int i =s; i < e; i++) {

            if(minI > map.get(z[i])){
                minI = map.get(z[i]);
                curr = i;
            }
        }
        if(minI == c.length){
            return null;
        }
//        System.out.println("index:"+minI);
        Node n = new Node(c[minI]);
        n.left = create(c,z,s,curr);
        n.right = create(c,z,curr+1,e);
        return n;
    }
    public static void prePrint(Node root){
        if(root !=null) {
            System.out.print(root.data + " ");
            prePrint(root.left);
            prePrint(root.right);
        }
    }
    public static void postPrint(Node root){
        if(root !=null) {

            postPrint(root.left);
            postPrint(root.right);
            System.out.print(root.data + " ");
        }
    }
    public static void leafPrint(Node root){
        if(root !=null) {
            if(root.left == null && root.right == null){
                System.out.print(root.data + " ");
            }
            leafPrint(root.left);
            leafPrint(root.right);

        }
    }
    public static void main(String[] args) {
    	String s1 = "3 5 4 2 6 7 1";
        String s2 = "2 5 3 6 4 7 1";
        
//        Scanner sc = new Scanner(System.in);
//        String s1 = sc.nextLine();
//        String s2 = sc.nextLine();

        map = new HashMap<Integer, Integer>();
        String[] items = s1.split(" ");
        String[] items2 = s2.split(" ");
        int[] c = new int[items.length];
        int[] z = new int[items.length];
        for (int i = 0; i < items.length; i++) {
            c[i] = Integer.parseInt(items[i]);
            z[i] = Integer.parseInt(items2[i]);
            map.put(c[i],i);
        }
        Node root = build(c,z);
        leafPrint(root);
        System.out.println();
        prePrint(root);
        System.out.println();
        postPrint(root);
        System.out.println();
    }
}

class  Node{
    public int data;
    Node left;
    Node right;
    public Node(int d){
        this.data = d;
    }
}