ABC345-C One Time Swap

問題へのリンク

C#のソース

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static string InputPattern = "InputX";

    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        if (InputPattern == "Input1") {
            WillReturn.Add("abc");
            //3
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("aaaaa");
            //1
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();
        string S = InputList[0];

        char[] CharArr = S.ToCharArray();
        long UB = CharArr.GetUpperBound(0);

        // 同じ文字の有無
        bool HasSameChar = true;
        if (CharArr.Length == CharArr.Distinct().Count()) {
            HasSameChar = false;
        }

        Dictionary<char, long> CntDict =
            CharArr.GroupBy(pX => pX).ToDictionary(pX => pX.Key, pX => pX.LongCount());

        long Answer = 0;
        for (long I = 0; I <= UB; I++) {
            char CurrChar = CharArr[I];
            foreach (var EachPair in CntDict) {
                if (EachPair.Key == CurrChar) continue;
                Answer += EachPair.Value;
            }
            CntDict[CurrChar]--;
        }

        if (HasSameChar) Answer++;
        Console.WriteLine(Answer);
    }
}

解説

最初に、GroupByとToDictionaryで文字ごとの件数を集計し、
左端を全探索してます。