思路：

public class Solution {
    public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
        TreeNode root=reConstructBinaryTree(pre,0,pre.length-1,in,0,in.length-1);
        return root;
    }
    private TreeNode reConstructBinaryTree(int[] pre,int startPre,int endPre,int[] in,int startIn, int endIn){
        if(startPre>endPre||startIn>endIn)
            return null;
        TreeNode root=new TreeNode(pre[startPre]);
        for(int i=startIn;i<=endIn;i++){
            if(in[i]==pre[startPre]){
root.left=reConstructBinaryTree(pre,startPre+1,startPre+i-startIn,in,startIn,i-1);//注意下標
root.right=reConstructBinaryTree(pre,i-startIn+startPre+1,endPre,in,i+1,endIn);
            }
        }
        return root;
    }
}