题目链接：重建二叉树

import java.util.*;/** public class TreeNode {*   int val = 0;*   TreeNode left = null;*   TreeNode right = null;*   public TreeNode(int val) {*     this.val = val;*   }* }*/public class Solution {/*** 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可*** @param preOrder int整型一维数组* @param vinOrder int整型一维数组* @return TreeNode类*/int [] pre = {0}, vin = {0};HashMap<Integer, Integer> map = new HashMap<>();public TreeNode reConstructBinaryTree (int[] preOrder, int[] vinOrder) {if (preOrder.length == 0 || vinOrder.length == 0) return null;this.pre = preOrder;this.vin = vinOrder;for (int i = 0; i < vin.length; i ++) map.put(vin[i], i);return dfs(0, pre.length - 1, 0, vin.length - 1);}public TreeNode dfs(int pl, int pr, int il, int ir) {if(pl > pr) return null;TreeNode root = new TreeNode(pre[pl]);int k = map.get(root.val);TreeNode left = dfs(pl + 1, pl + k - il, il, k - 1);TreeNode right = dfs(pl + k - il + 1, pr, k + 1, ir);root.left = left;root.right = right;return root;}
}