如何用C#实现CCC 2018 J3城市间距离计算程序？

Problem Overview #

The task requires calculating pairwise distances between 5 cities, given consecutive distances between adjacent cities. The expected output is a 5x5 grid where each entry represents the distance from one city to another.

Issues with Your Original Code #

• Return Type Mismatch: The method returns an int, but we need a multi-line string for the distance grid output.
• Incorrect List Initialization: List<int> cities = new List<int> {5}; creates a list with one element (5) instead of a list sized for 5 cities.
• Early Returns: Multiple return statements inside loops halt execution before completing all distance calculations.
• Index Errors: Accessing cities[i-1] when i=0 causes out-of-bounds errors, and references like cities[i+5] are invalid for a 5-city list.
• Confused Logic: The code mixes cumulative distance building and pairwise computation, leading to incorrect results.

Corrected Code #

/// GET/api/J3/DistanceCalculator/{distance1}/{distance2}/{distance3}/{distance4} 
/// api/J3/DistanceCalculator/3/10/12/5 
/// Output:
/// 0/3/13/25/30
/// 3/0/10/22/27
/// 13/10/0/12/17
/// 25/22/12/0/5
/// 30/27/17/5/0
/// </example>

// GET api/J3/DistanceCalculator/{distance1}/{distance2}/{distance3}/{distance4}/
[HttpGet]
[Route("api/J3/DistanceCalculator/{distance1}/{distance2}/{distance3}/{distance4}")]
public string DistanceCalculator(int distance1, int distance2, int distance3, int distance4)
{
    // Build cumulative distances from city 0 to each city
    int[] cityDistances = new int[5];
    cityDistances[0] = 0;
    cityDistances[1] = distance1;
    cityDistances[2] = cityDistances[1] + distance2;
    cityDistances[3] = cityDistances[2] + distance3;
    cityDistances[4] = cityDistances[3] + distance4;

    List<string> resultLines = new List<string>();

    // Generate each line of the distance grid
    for (int startCity = 0; startCity < 5; startCity++)
    {
        List<string> lineEntries = new List<string>();
        for (int endCity = 0; endCity < 5; endCity++)
        {
            // Calculate distance between start and end city (absolute difference)
            int distance = Math.Abs(cityDistances[endCity] - cityDistances[startCity]);
            lineEntries.Add(distance.ToString());
        }
        // Join entries with '/' and add to result
        resultLines.Add(string.Join("/", lineEntries));
    }

    // Join all lines with newline characters
    return string.Join("\n", resultLines);
}

Key Improvements #

1. Cumulative Distance Array: First compute total distances from city 0 to every other city. Pairwise distance becomes the absolute difference between two cumulative values.
2. Proper Return Type: The method now returns a string matching the required output format.
3. Clear Nested Loops: Outer loop iterates over starting cities, inner loop calculates distances to all other cities, building each output line.
4. Correct Formatting: Uses string.Join to create /-separated entries per line and \n to separate lines in the final output.

内容的提问来源于stack exchange，提问作者Bea