题解 | #从前序和中序遍历构造二叉树#

善用Java的工具类

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param preorder int整型一维数组 
     * @param inorder int整型一维数组 
     * @return TreeNode类
     */
    public TreeNode buildTree (int[] preorder, int[] inorder) {
        // write code here
        if(preorder.length==0||inorder.length==0)
            return null;

        TreeNode root = new TreeNode(preorder[0]);

        int mid = 0;
        for(int i = 0 ; i < inorder.length ; i++){
            if(inorder[i]== preorder[0])
                mid = i;
        }

        root.left = buildTree(Arrays.copyOfRange(preorder,1,mid + 1),Arrays.copyOfRange(inorder,0,mid));
        root.right = buildTree(Arrays.copyOfRange(preorder,mid + 1,preorder.length),Arrays.copyOfRange(inorder,mid + 1,inorder.length));

        return root;
    }
}