典型90問 048 I will not drop out（★3）

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("4 3");
            WillReturn.Add("4 3");
            WillReturn.Add("9 5");
            WillReturn.Add("15 8");
            WillReturn.Add("8 6");
            //21
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("2 2");
            WillReturn.Add("7 6");
            WillReturn.Add("3 2");
            //8
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("10 12");
            WillReturn.Add("987753612 748826789");
            WillReturn.Add("36950727 36005047");
            WillReturn.Add("961239509 808587458");
            WillReturn.Add("905633062 623962559");
            WillReturn.Add("940964276 685396947");
            WillReturn.Add("959540552 928301562");
            WillReturn.Add("60467784 37828572");
            WillReturn.Add("953685176 482123245");
            WillReturn.Add("87983282 66762644");
            WillReturn.Add("912605260 709048491");
            //6437530406
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    struct ABInfoDef
    {
        internal long A;
        internal long B;
    }
    static List<ABInfoDef> mABInfoList = new List<ABInfoDef>();

    static void Main()
    {
        List<string> InputList = GetInputList();

        long[] wkArr = { };
        Action<string> SplitAct = pStr =>
            wkArr = pStr.Split(' ').Select(pX => long.Parse(pX)).ToArray();

        SplitAct(InputList[0]);
        long K = wkArr[1];

        foreach (string EachStr in InputList.Skip(1)) {
            SplitAct(EachStr);
            ABInfoDef WillAdd;
            WillAdd.A = wkArr[0];
            WillAdd.B = wkArr[1];
            mABInfoList.Add(WillAdd);
        }

        var ScoreList = new List<long>();
        foreach (ABInfoDef EachABInfo in mABInfoList) {
            ScoreList.Add(EachABInfo.B);
            ScoreList.Add(EachABInfo.A - EachABInfo.B);
        }

        var Query = ScoreList.OrderByDescending(pX => pX).Take((int)K);
        Console.WriteLine(Query.Sum());
    }
}

解説

考察すれば貪欲法が使えると分かります。