题解 | 牛牛的考试

using System;
using System.Linq;
using System.Collections.Generic;
using System.Text;
public class Program {
    public static void Main() {
        int X = Convert.ToInt32(Console.ReadLine());
        string result = "";

        Console.ReadKey();
        Console.ReadKey();

        for (int i = 0; i < X; i++) {
            // string[] inputs = new string[4];
            // for (int j = 0; j < 4; j++) {
            // inputs[j] = Console.ReadLine();
            // }
            List<string> inputs = new List<string>();
            string[] prefixes = {"A.", "B.", "C.", "D."};

            for (int j = 0; j < prefixes.Length; j++) {

                // StringBuilder input = new StringBuilder(ReadStringWithPrefix(
                        // prefixes[(j + 1) % 4]));
                StringBuilder input = new StringBuilder(Console.ReadLine());
                input.Insert(0, prefixes[j]);
                string inputt = input.ToString();
                inputs.Add(inputt);
            }

            int[] lengths = inputs.Select(s => s.Length).ToArray();

            int maxLength = lengths.Max();
            int maxCount = lengths.Count(l => l == maxLength);

            int minLength = lengths.Min();
            int minCount = lengths.Count(l => l == minLength);

            char recordChar;

            if (maxCount == 1 && minCount != 1) { // 唯一最大
                int maxIndex = Array.IndexOf(lengths, maxLength);
                recordChar = inputs[maxIndex][0];
            } else if (minCount == 1 && maxCount != 1) { // 唯一最小
                int minIndex = Array.IndexOf(lengths, minLength);
                recordChar = inputs[minIndex][0];
            } else { // 非唯一最大或最小
                recordChar = 'C';
            }

            result += recordChar;
        }

        foreach (char c in result) {
            Console.WriteLine(c);
        }
    }

//     private static string ReadStringWithPrefix(String prefix) {
//         string input = "";
//         string line;
//         bool isReading = false;
//         //读取所有行
//         while ((line = Console.ReadLine()) != null) {
//             if (line.StartsWith(prefix, StringComparison.Ordinal)) {
//                 isReading = true;
//             } else {
//                 input += "\n" + line;
//             }

//             if (line.StartsWith("A.", StringComparison.Ordinal) ||
//                     line.StartsWith("B.", StringComparison.Ordinal) ||
//                     line.StartsWith("C.", StringComparison.Ordinal) ||
//                     line.StartsWith("D.", StringComparison.Ordinal)) {
//                 break;
//             }
//         }
//         return input;
//     }
}