树之105 Construct Binary Tree from Preorder and Inorder Traversal

题目链接：https://leetcode-cn.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/

参考链接：https://blog.csdn.net/qq_36172443/article/details/81105258

　　　　　https://www.lintcode.com/problem/clone-binary-tree/description

　　　　　https://www.cnblogs.com/phdeblog/p/9309219.html

首先你得理解如何递归建立一颗二叉树，然后才能理解本题。网上有很多解法都是通过变化中序遍历和前序续遍历的index来求解本题，这样的解法很容易弄错。如何变化index这是一个难点，该解法通过数组copy避免了计算index。

    public TreeNode buildTree(int[] pre, int[] in) {
        if (pre.length == 0) {
            return null;
        }
        int i = 0;
        for (; i < in.length; i++) {
            if (pre[0] == in[i]) {
               break;
            }
        }
        TreeNode node = new TreeNode(pre[0]);
        //[1,i] [0,i-1]
        //[i+1,length-1] [i+1,length-1]
        node.left = buildTree(
                Arrays.copyOfRange(pre, 1, i + 1),
                Arrays.copyOfRange(in, 0, i));
        node.right = buildTree(
                Arrays.copyOfRange(pre, i + 1, pre.length),
                Arrays.copyOfRange(in, i + 1, in.length));
        return node;

    }