注意:你可以假设树中没有重复的元素。

思路

（1）参见剑指Offer-树-面试题7：重建二叉树

解法1

执行用时 :22 ms, 在所有 Java 提交中击败了12.68%的用户
内存消耗 :43.5 MB, 在所有 Java 提交中击败了10.24%的用户

class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        return buildTree(preorder, 0, preorder.length-1, inorder, 0, inorder.length-1);   
    }

    TreeNode buildTree(int[] preorder, int preStart, int preEnd, int[] inorder, int inStart, int inEnd){

        //if(preStart >= preEnd || inStart >= inEnd ){  errror1
        if(preStart > preEnd || inStart > inEnd ){
            return null;
        }

        int index = inStart;
        while(preorder[preStart] != inorder[index] && index < inEnd){
            index++;
        }

        TreeNode root = new TreeNode(inorder[index]);
        int len = index - inStart;
        root.left = buildTree(preorder, preStart+1, preStart+len, inorder, inStart, index-1);
        root.right = buildTree(preorder, preStart+len+1, preEnd, inorder, index+1, inEnd);

        return root;
    }
}