算法题--01

import java.util.HashMap;
public class Solution {
    public int[] pre;
    public int[] mid;
    public HashMap<Integer ,Integer> map=new HashMap<>();
    public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
        this.pre=pre;
        this.mid=in;
        for(int i=0;i<in.length;i++){
            map.put(in[i],i);
        }
        
        return pre(0,pre.length-1,0,in.length-1);
    }
    public TreeNode pre(int pi,int pj,int mi,int mj){
        if(mi>mj||pi>pj)
            return null;
        TreeNode node=new TreeNode(pre[pi]);
        int index=map.get(pre[pi]);
        node.left=pre(pi+1,pi+index-mi,mi,index-1);
        node.right=pre(pi+index-mi+1,pj,index+1,mj);
        return node;
        
    }
}