递归写法

import java.util.*;
/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {

    private static int index = 0;

    private TreeNode reConstructBinaryTree(int [] pre,int [] vin, int left, int right) {
        if (index == pre.length) return null;
        if (left > right) return null;

        for (int i = left; i <= right; i ++ ) {
            if (pre[index] == vin[i]) {
                TreeNode newNode = new TreeNode(pre[index ++ ]);
                newNode.left = reConstructBinaryTree(pre, vin, left, i);
                newNode.right = reConstructBinaryTree(pre, vin, i + 1 , right);
                return newNode;
            }
        }
        return null;
    }

    public TreeNode reConstructBinaryTree(int [] pre,int [] vin) {
        int len = pre.length;
        return reConstructBinaryTree(pre, vin, 0, pre.length - 1);
    }
}