重建二叉树

import java.util.*;
/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    int[] preorder;
    HashMap<Integer, Integer> dic = new HashMap<>();
    public TreeNode reConstructBinaryTree(int [] pre,int [] vin) {
        this.preorder = pre;
        for(int i = 0; i < pre.length;i++)
            dic.put(vin[i], i);
        return recur(0, 0,  vin.length -1);
    }
    TreeNode recur(int root, int left, int right){
        if(left > right) return null;
        TreeNode node = new TreeNode(preorder[root]);
        int i = dic.get(preorder[root]);
        node.left = recur(root + 1, left, i - 1);
        node.right = recur(root + 1 - left +i, i+1 ,right);
        return node;
    }
}