ABC188-E Peddler

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("2 3 1 5");
            WillReturn.Add("2 4");
            WillReturn.Add("1 2");
            WillReturn.Add("1 3");
            //3
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("5 5");
            WillReturn.Add("13 8 3 15 18");
            WillReturn.Add("2 4");
            WillReturn.Add("1 2");
            WillReturn.Add("4 5");
            WillReturn.Add("2 3");
            WillReturn.Add("1 3");
            //10
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("3 1");
            WillReturn.Add("1 100 1");
            WillReturn.Add("2 3");
            //-99
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static Dictionary<int, int> mADict = new Dictionary<int, int>();

    // 隣接リストで枝を管理
    static Dictionary<int, List<int>> mToNodeListDict = new Dictionary<int, List<int>>();

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

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

        SplitAct(InputList[1]);
        for (int I = 0; I <= wkArr.GetUpperBound(0); I++) {
            mADict[I + 1] = wkArr[I];
        }

        foreach (string EachStr in InputList.Skip(2)) {
            SplitAct(EachStr);
            int FromNode = wkArr[0];
            int ToNode = wkArr[1];

            if (mToNodeListDict.ContainsKey(FromNode) == false) {
                mToNodeListDict[FromNode] = new List<int>();
            }
            mToNodeListDict[FromNode].Add(ToNode);
        }

        Solve();
    }

    struct JyoutaiDef
    {
        internal int Level;
        internal int CurrNode;
    }

    // 貪欲法で、金が一番安いノードからDFSを繰り返す(再訪防止で枝切りする)
    static void Solve()
    {
        var VisitedSet = new HashSet<int>();
        int Answer = int.MinValue;
        foreach (var EachPair in mADict.OrderBy(pX => pX.Value)) {
            JyoutaiDef WillPush;
            WillPush.Level = 0;
            WillPush.CurrNode = EachPair.Key;

            var Stk = new Stack<JyoutaiDef>();
            Stk.Push(WillPush);
            while (Stk.Count > 0) {
                JyoutaiDef Popped = Stk.Pop();

                if (Popped.Level >= 1) {
                    Answer = Math.Max(Answer, mADict[Popped.CurrNode] - EachPair.Value);
                }

                if (mToNodeListDict.ContainsKey(Popped.CurrNode) == false) {
                    continue;
                }
                foreach (int EachInt in mToNodeListDict[Popped.CurrNode]) {
                    // 再訪防止で枝切り
                    if (VisitedSet.Add(EachInt) == false) continue;

                    WillPush.Level = Popped.Level + 1;
                    WillPush.CurrNode = EachInt;
                    Stk.Push(WillPush);
                }
            }
        }
        Console.WriteLine(Answer);
    }
}

解説

貪欲法で、金が一番安いノードからDFSを繰り返してます。
再訪防止で枝切りもしてます。