第8回PAST H 最短経路

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 5");
            WillReturn.Add("1 2 3");
            WillReturn.Add("1 3 2");
            //Yes
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("3 4");
            WillReturn.Add("1 2 3");
            WillReturn.Add("1 3 2");
            //No
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("10 15");
            WillReturn.Add("3 8 3");
            WillReturn.Add("5 9 3");
            WillReturn.Add("6 7 1");
            WillReturn.Add("7 8 1");
            WillReturn.Add("2 8 5");
            WillReturn.Add("2 4 5");
            WillReturn.Add("4 9 3");
            WillReturn.Add("1 4 5");
            WillReturn.Add("1 10 2");
            //Yes
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static long mN;
    static long mX;

    struct EdgeInfoDef
    {
        internal long ToNode;
        internal long Cost;
    }
    static Dictionary<long, List<EdgeInfoDef>> mEdgeInfoListDict = new Dictionary<long, List<EdgeInfoDef>>();

    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]);
        mN = wkArr[0];
        mX = wkArr[1];

        foreach (string EachStr in InputList.Skip(1)) {
            SplitAct(EachStr);
            long A = wkArr[0];
            long B = wkArr[1];
            long C = wkArr[2];

            Action<long, long, long> AddEdgeAct = (pFromNode, pToNode, pCost) =>
            {
                if (mEdgeInfoListDict.ContainsKey(pFromNode) == false) {
                    mEdgeInfoListDict[pFromNode] = new List<EdgeInfoDef>();
                }
                EdgeInfoDef WillAdd;
                WillAdd.ToNode = pToNode;
                WillAdd.Cost = pCost;
                mEdgeInfoListDict[pFromNode].Add(WillAdd);
            };
            AddEdgeAct(A, B, C);
            AddEdgeAct(B, A, C);
        }

        for (long I = 1; I <= mN; I++) {
            bool HasAnswer = ExecBFS(I);
            if (HasAnswer) {
                Console.WriteLine("Yes");
                return;
            }
        }
        Console.WriteLine("No");
    }

    struct JyoutaiDef
    {
        internal long CurrNode;
        internal long CostSum;
    }

    static bool ExecBFS(long pStaNode)
    {
        var Que = new Queue<JyoutaiDef>();
        JyoutaiDef WillEnquue;
        WillEnquue.CurrNode = pStaNode;
        WillEnquue.CostSum = 0;
        Que.Enqueue(WillEnquue);

        var VisitedSet = new HashSet<long>();
        VisitedSet.Add(pStaNode);

        while (Que.Count > 0) {
            JyoutaiDef Dequeued = Que.Dequeue();

            // クリア判定
            if (Dequeued.CostSum == mX) {
                return true;
            }

            // 枝切り
            if (Dequeued.CostSum > mX) {
                continue;
            }

            if (mEdgeInfoListDict.ContainsKey(Dequeued.CurrNode) == false) {
                continue;
            }
            foreach (EdgeInfoDef EachEdgeInfo in mEdgeInfoListDict[Dequeued.CurrNode]) {
                if (VisitedSet.Add(EachEdgeInfo.ToNode) == false) {
                    continue;
                }
                WillEnquue.CurrNode = EachEdgeInfo.ToNode;
                WillEnquue.CostSum = Dequeued.CostSum + EachEdgeInfo.Cost;
                Que.Enqueue(WillEnquue);
            }
        }
        return false;
    }
}

解説

ナイーブに全てのノードから幅優先探索してます。