Day4 剑指offer：重建二叉树

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。假设输入的前序遍历和中序遍历的结果中都不含重复的数字。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并返回。

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
        return reConstructBT(pre, 0, pre.length-1, in, 0, in.length-1);
    }
    
    public TreeNode reConstructBT(int[] pre, int preStart, int preEnd, int[] in, int inStart, int inEnd){
        if(preStart > preEnd || inStart > inEnd){
            return null;
        }
        
        TreeNode node = new TreeNode(pre[preStart]);
        
        for(int i=inStart; i<=inEnd; i++){
            if(in[i] == pre[preStart]){
                node.left = reConstructBT(pre, preStart+1, preStart+i-inStart, in, inStart, i-1);
                node.right = reConstructBT(pre, preStart+i-inStart+1, preEnd, in, i+1, inEnd);
                break;
            }
        }
        
        return node;
    }
}