מריה בוטוסוב

כלל הקידוד הוא: k[encoded_string] לדוגמא: s = "3[a2[c]]", return "accaccacc";

public string DecodeString(string s) {
    string result = String.Empty;
    Stack<string> strStack = new Stack<string>();
    Stack<int> countStack = new Stack<int>();
    int i = 0;
    while(i < s.Length){
        if(char.IsDigit(s[i])) {
            int number = s[i++] - '0'; 
            while(char.IsDigit(s[i])) {
                number = 10 * number + s[i++] - '0';
            }
            countStack.Push(number);
        }
        else if(s[i] == '[') {
            strStack.Push(result);
            result = String.Empty;
            i++;
        }
        else if(s[i] == ']') {
            StringBuilder sb = new StringBuilder();
            int numOfTimes = countStack.Pop();
            for(int y=0; y<numOfTimes;y++) {
                sb.Append(result);
            }
            result = strStack.Pop() + sb.ToString();
            i++;
        }
        else {
            result+=s[i++];
        }
    }
    return result;
}