重建二叉树

public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
        if (pre==null || in==null) return null;
        return dfs(pre,0,pre.length-1,in,0,in.length-1);
    }

    private TreeNode dfs(int[] pre, int ps, int pe, int[] in, int ins, int ine) {
        //一般发生在pre下标ps或者pe的值处于in在区间ins和ine的两端处
        if (ps>pe || ins>ine) return null;
        if (ps==pe) {
            TreeNode tn=new TreeNode(pre[ps]);
            return tn;
        }
        int temp = pre[ps];
        int index = getIndex(temp,in,ins,ine);
        //ins index-1 左子树   index+1   ine 右子树
        //ps+1 ps+1+index-1-ins=index+ps-ins 左子树   index+ps-ins+1 pe右子树
        TreeNode left = dfs(pre,ps+1,index+ps-ins,in,ins,index-1);
        TreeNode right = dfs(pre,index+ps-ins+1,pe,in,index+1,ine);
        TreeNode root = new TreeNode(temp);
        root.left=left;
        root.right=right;
        return root;
    }

    private int getIndex(int temp,int[] in, int ins, int ine) {
        for (int i=ins;i<=ine;i++){
            if(in[i]==temp){
                return i;
            }
        }
        return 0;
    }