Construct Binary Tree from Preorder and Inorder Traversal

题目描述：

Given preorder and inorder traversal of a tree, construct the binary tree.

Note:
You may assume that duplicates do not exist in the tree.

给定先序遍历和中序遍历序列，还原树。

一次AC，代码如下：

public class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        if(preorder==null||preorder.length==0)
        	return null;
        return buildRoot(preorder, 0, preorder.length-1, inorder, 0, inorder.length-1);
    }
	
	public int findIndex(int[] inorder,int target){
		for(int i=0;i<inorder.length;i++){
			if(inorder[i]==target)
				return i;
		}
		return 0;
	}
	
	public TreeNode buildRoot(int[] preorder,int preleft,int preright,int[] inorder,int inleft,int inright){
		if(preleft==preright)
			return new TreeNode(preorder[preleft]);
		if(preleft>preright)
			return null;
		TreeNode root=new TreeNode(preorder[preleft]);
		int index=findIndex(inorder, preorder[preleft]);
		root.left=buildRoot(preorder, preleft+1, preleft+index-inleft, inorder, inleft, index-1);
		root.right=buildRoot(preorder, preleft+index-inleft+1, preright, inorder, index+1, inright);
		return root;
	}
}