ABC018-D バレンタインデー

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("3 4 2 3 7");
            WillReturn.Add("1 1 9");
            WillReturn.Add("1 2 7");
            WillReturn.Add("1 3 15");
            WillReturn.Add("1 4 6");
            WillReturn.Add("2 2 3");
            WillReturn.Add("2 4 6");
            WillReturn.Add("3 3 6");
            //37
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("4 5 3 2 9");
            WillReturn.Add("2 3 5");
            WillReturn.Add("3 1 4");
            WillReturn.Add("2 2 2");
            WillReturn.Add("4 1 9");
            WillReturn.Add("3 5 3");
            WillReturn.Add("3 3 8");
            WillReturn.Add("1 4 5");
            WillReturn.Add("1 5 7");
            WillReturn.Add("2 4 8");
            //26
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    struct XYZInfoDef
    {
        internal int X;
        internal int Y;
        internal int Z;
    }

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

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

        SplitAct(InputList[0]);
        int N = wkArr[0];
        int M = wkArr[1];
        int P = wkArr[2];
        int Q = wkArr[3];

        var XYZInfoList = new List<XYZInfoDef>();
        foreach (string EachStr in InputList.Skip(1)) {
            SplitAct(EachStr);
            XYZInfoDef WillAdd;
            WillAdd.X = wkArr[0];
            WillAdd.Y = wkArr[1];
            WillAdd.Z = wkArr[2];
            XYZInfoList.Add(WillAdd);
        }

        // 女子N人からP人の選び方を全探索
        List<HashSet<int>> SelectedSetList = ExecDFS(N, P);

        int Answer = int.MinValue;
        foreach (HashSet<int> EachSelectedSet in SelectedSetList) {
            var tmp1 = XYZInfoList.FindAll(pX => EachSelectedSet.Contains(pX.X));
            var tmp2 = tmp1.GroupBy(pX => pX.Y);
            var tmp3 = tmp2.Select(pX => pX.Sum(pY => pY.Z));
            var tmp4 = tmp3.OrderByDescending(pX => pX);
            var tmp5 = tmp4.Take(Q).Sum();
            Answer = Math.Max(Answer, tmp5);
        }
        Console.WriteLine(Answer);
    }

    struct JyoutaiDef
    {
        internal int CurrVal;
        internal HashSet<int> SelectedSet;
    }

    // 女子N人からP人の選び方を全探索
    static List<HashSet<int>> ExecDFS(int pN, int pP)
    {
        var WillReturn = new List<HashSet<int>>();

        var Stk = new Stack<JyoutaiDef>();
        JyoutaiDef WillPush;
        WillPush.CurrVal = 1;
        WillPush.SelectedSet = new HashSet<int>();
        Stk.Push(WillPush);

        while (Stk.Count > 0) {
            JyoutaiDef Popped = Stk.Pop();

            // クリア判定
            if (Popped.SelectedSet.Count == pP) {
                WillReturn.Add(Popped.SelectedSet);
                continue;
            }

            for (int I = Popped.CurrVal; I <= pN; I++) {
                WillPush.CurrVal = I + 1;
                WillPush.SelectedSet = new HashSet<int>(Popped.SelectedSet);
                WillPush.SelectedSet.Add(I);
                Stk.Push(WillPush);
            }
        }
        return WillReturn;
    }
}

解説

半分全探索で解いてます。