ABC121-C Energy Drink Collector

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("2 5");
            WillReturn.Add("4 9");
            WillReturn.Add("2 4");
            //12
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("4 30");
            WillReturn.Add("6 18");
            WillReturn.Add("2 5");
            WillReturn.Add("3 10");
            WillReturn.Add("7 9");
            //130
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("1 100000");
            WillReturn.Add("1000000000 100000");
            //100000000000000
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

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

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

        SplitAct(InputList[0]);
        int M = wkArr[1];

        var ABList = new List<int[]>();
        foreach (string EachStr in InputList.Skip(1)) {
            SplitAct(EachStr);
            ABList.Add(wkArr);
        }

        long Answer = 0;
        long BoughtCnt = 0;
        foreach (int[] EachAB in ABList.OrderBy(X => X[0])) {
            for (int I = 1; I <= EachAB[1]; I++) {
                Answer += EachAB[0];
                if (++BoughtCnt == M) {
                    Console.WriteLine(Answer);
                    return;
                }
            }
        }
    }
}

解説

貪欲法で解いてます。