二叉树

前序遍历：ABDFCEGH

中序遍历：BFDAGEHC

演示

代码：

package com.fdw.algorithm.hhh;

import com.fdw.algorithm.structure.TreeNode;

import java.util.LinkedList;
import java.util.Queue;

/**
 * @description:
 * @author: ThatMonth
 * @create: 2024-08-20 13:54
 **/
public class Test55 {
    public static void main(String[] args) {
        //前序遍历
        String beforeOrder = "ABDFCEGH";
        //中序遍历
        String midOrder = "BFDAGEHC";
        //构建二叉树
        TreeNode execute = execute(beforeOrder, midOrder, 0, beforeOrder.length() - 1, 0, midOrder.length() - 1);
        //层序遍历
        levelPrint(execute);
    }
    //中左右 左中右
    public static TreeNode execute(String beforeOrder,String midOrder,int bh,int bt,int mh,int mt){
        if(bh>bt||mh>mt){
            return null;
        }
        //前序第一个是顶
        char rootc = beforeOrder.charAt(bh);
        TreeNode root = new TreeNode(rootc);

        int midindex=mh;
        int temp =0;
        //从中序中找到顶
        for (int i = mh; i <= mt; i++) {
            if(midOrder.charAt(i)==rootc){
                midindex = i;
                break;
            }
            temp++;
        }
        root.left = execute(beforeOrder,midOrder, bh+1, bh+temp, mh, midindex-1);
        root.right = execute(beforeOrder,midOrder, bh+temp+1, bt, midindex+1, mt);
        return root;
    }

    //层序遍历
    public static void levelPrint(TreeNode node){
        Queue<TreeNode> queue =new LinkedList<>();
        queue.add(node);
        while(!queue.isEmpty()){
            TreeNode poll = queue.poll();
            System.out.print(poll.ch+" ");
            if(poll.left!=null){
                queue.offer(poll.left);
            }
            if(poll.right!=null){
                queue.offer(poll.right);
            }
        }
    }
}