Leetcode 604: Design Compressed String Iterator

Design and implement a data structure for a compressed string iterator. It should support the following operations: next and hasNext.

The given compressed string will be in the form of each letter followed by a positive integer representing the number of this letter existing in the original uncompressed string.

next() - if the original string still has uncompressed characters, return the next letter; Otherwise return a white space.
hasNext() - Judge whether there is any letter needs to be uncompressed.

Note:
Please remember to RESET your class variables declared in StringIterator, as static/class variables are persisted across multiple test cases. Please see here for more details.

Example:

StringIterator iterator = new StringIterator("L1e2t1C1o1d1e1");

iterator.next(); // return 'L'
iterator.next(); // return 'e'
iterator.next(); // return 'e'
iterator.next(); // return 't'
iterator.next(); // return 'C'
iterator.next(); // return 'o'
iterator.next(); // return 'd'
iterator.hasNext(); // return true
iterator.next(); // return 'e'
iterator.hasNext(); // return false
iterator.next(); // return ' '

public class StringIterator {

    private string str = "";
    private int cur = 0;
    private char curChar = ' ';
    private int curCount = 0;
    
    public StringIterator(string compressedString) {
        this.str = compressedString;
    }
    
    public char Next() { 
        if (curCount > 0)
        {
            curCount--;
            return curChar;
        }
        else if (cur >= str.Length)
        {
            return ' ';
        }
        else
        {
            curChar = str[cur];
            cur++;
            
            curCount = 0;
            
            while (cur < str.Length && Char.IsDigit(str[cur]))
            {
                curCount = curCount * 10 + (int)str[cur] - (int)'0';
                cur++;
            }
            
            curCount--;
            return curChar;
        }
    }
    
    public bool HasNext() {
        return curCount > 0 || cur < str.Length;
    }
}

/**
 * Your StringIterator object will be instantiated and called as such:
 * StringIterator obj = new StringIterator(compressedString);
 * char param_1 = obj.Next();
 * bool param_2 = obj.HasNext();
 */