Quipu

Used In: SRM 155
Used As: Division II Level One

Problem Statement

The Incas used a sophisticated system of record keeping consisting of bundles of knotted cords. Such a bundle of cords is called a quipu. Each individual cord represents a single number. Surprisingly, the Incas used a base-10 positional system, just like we do today. Each digit of a number is represented by a cluster of adjacent knots, with spaces between neighboring clusters. The digit is determined by the number of knots in the cluster. For example, the number 243 would be represented by a cord with knots tied in the following pattern

 -XX-XXXX-XXX-

where each uppercase 'X' represents a knot and each '-' represents an unknotted segment of cord (all quotes for clarity only).

Unlike many ancient civilizations, the Incas were aware of the concept of zero, and used it in their quipus. A zero is represented by a cluster containing no knots. For example, the number 204003 would be represented by a cord with knots tied in the following pattern

 -XX--XXXX---XXX-
    ^^    ^^^
    ^^    ^^^
    ^^    two zeros between these three segments
    ^^
    one zero between these two segments

Notice how adjacent dashes signal the presence of a zero.
Your task is to translate a single quipu cord into an integer. The cord will be given as a String knots containing only the characters 'X' and '-'. There will be a single '-' between each cluster of 'X's, as well as a leading '-' and a trailing '-'. The first cluster will not be empty.

Definition

Class: Quipu
Method: readKnots
Parameters: String
Returns: int
Method signature: int readKnots(String knots)
(be sure your method is public)

Constraints

• knots contains between 3 and 50 characters, inclusive.
• knots contains only the characters 'X' and '-'. Note that 'X' is uppercase.
• The first and last characters of knots are '-'s. The second character is 'X'.
• knots does not contain 10 consecutive 'X's.
• knots will represent a number between 1 and 1000000, inclusive.

Examples

1. "-XX-XXXX-XXX-"
   Returns: 243
   The first example above.

2. "-XX--XXXX---XXX-"
   Returns: 204003
   The second example above.

3. "-X-"
   Returns: 1

4. "-X-------"
   Returns: 1000000

5. "-XXXXXXXXX--XXXXXXXXX-XXXXXXXXX-XXXXXXX-XXXXXXXXX-"
   Returns: 909979

#include <iostream>
#include <string>

using namespace std;

class Quipu {  
    public:
        int readKnots(string knots) {
            int countX = 0,
                num = 0;
            for (int i = 0; i < knots.size(); ++i) {
                if (knots[i] == 'X') {
                    ++countX;
                } else {
                    num *= 10;
                    num += countX;
                    countX = 0;
                }
            }
            return num;
        }
};