重建二叉树

题目：

输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。

解答：

public class Solution {

    public static TreeNode reConstructBinaryTree(int[] pre, int[] in) {
        if(pre == null || in == null || pre.length != in.length) {
            return null;
        }

        return createTree(pre, 0, pre.length-1, in, 0, in.length-1);
    }

    private static TreeNode createTree(int[] pre, int preStart, int preEnd, int inStart, int inEnd) {
        if(preStart > preEnd || inStart > inEnd) {
            return null;
        }

        TreeNode root = new TreeNode(pre[preStart]);
        root.left = root.right = null;

        for(int i = 0; i <= inEnd; i++) {
            if(pre[preStart] == in[i]) {
                root.left = createTree(pre, preStart+1,preStart+i-inStart, in, inStart, i-1);

                root.right = createTree(pre, preStart+i-inStart+1, preEnd, in, i+1, inEnd);
            }
        }

        return root;
    }
}