class Solution {
    public TreeNode recoverFromPreorder(String S) {
        int start = 0;
        //查找数字
        for (; start < S.length(); start++) {
            if (S.charAt(start) == '-') {
                break;
            }
        }
        String ss = S.substring(0,start);
        //System.out.println(ss);
        TreeNode root = new TreeNode(Integer.valueOf(ss));
        //index每次位置是数字的位置，1-2--3,这一步让index在0位置
        index = start - 1;
        root.left = fun(S,0);
        root.right = fun(S,0);
        return root;
    }
    private int index = 0;//index记录坐标
    public TreeNode fun(String s,int depth) {
        int c = getNextDepth(s,index);
        if (c <= depth || index > s.length() - 1) return null;
        //更新depth，在数字位置上面，而不是'-'。对于1-2--3，index这时应该在2位置
        index += (c +1);
        //查找数字
        int a = index;
        for (; a < s.length(); a++) {
            if (s.charAt(a) == '-') {
                break;
            }
        }
        String ns = s.substring(index,a);
        //System.out.println("ns = "+ns+" index = "+index+" a = "+a);
        int num = Integer.valueOf(ns);
        TreeNode now = new TreeNode(num);
        index = a - 1;
        now.left = fun(s,c);
        now.right = fun(s,c);
        return now;
    }
    public int getNextDepth(String s,int ind) {
        int c = 0;
        for (int i = ind + 1; i < s.length(); i++) {
            if (s.charAt(i) == '-') {
                c++;
            } else {
                break;
            }
        }
        return c;
    }
}