ALDS1_11_B: Depth First Search

問題へのリンク

C#のソース

using System;
using System.Collections.Generic;
using System.Linq;

// Q037 深さ優先探索 https://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_11_B&lang=jp
class Program
{
    static string InputPattern = "InputX";

    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        if (InputPattern == "Input1") {
            WillReturn.Add("4");
            WillReturn.Add("1 1 2");
            WillReturn.Add("2 1 4");
            WillReturn.Add("3 0");
            WillReturn.Add("4 1 3");
            //1 1 8
            //2 2 7
            //3 4 5
            //4 3 6
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("6");
            WillReturn.Add("1 2 2 3");
            WillReturn.Add("2 2 3 4");
            WillReturn.Add("3 1 5");
            WillReturn.Add("4 1 6");
            WillReturn.Add("5 1 6");
            WillReturn.Add("6 0");
            //1 1 12
            //2 2 11
            //3 3 8
            //4 9 10
            //5 4 7
            //6 5 6
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    struct JyoutaiDef
    {
        internal int CurrNode;
    }

    // 隣接リスト
    static Dictionary<int, int[]> mToNodeArrDict = new Dictionary<int, int[]>();

    static void Main()
    {
        List<string> InputList = GetInputList();
        int N = int.Parse(InputList[0]);

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

        foreach (string EachStr in InputList.Skip(1)) {
            SplitAct(EachStr);
            int NodeID = wkArr[0];
            int[] ToNodeArr = EachStr.Split(' ').Skip(2).Select(pX => int.Parse(pX)).ToArray();

            mToNodeArrDict[NodeID] = ToNodeArr;
        }

        for (int I = 1; I <= N; I++) {
            if (mFindTimeDict.ContainsKey(I) == false) {
                ExecDFS(I);
            }
        }

        for (int I = 1; I <= N; I++) {
            Console.WriteLine("{0} {1} {2}", I, mFindTimeDict[I], mEndTimeDict[I]);
        }
    }

    // 現在時間
    static int mCurrTime = 1;

    // 最初に訪問した、発見時刻のDict
    static Dictionary<int, int> mFindTimeDict = new Dictionary<int, int>();

    // 隣接リストを調べ終えた、完了時刻のDict
    static Dictionary<int, int> mEndTimeDict = new Dictionary<int, int>();

    // 深さ優先探索を行う
    static void ExecDFS(int pStartNode)
    {
        var Stk = new Stack<JyoutaiDef>();
        JyoutaiDef WillPush;
        WillPush.CurrNode = pStartNode;
        Stk.Push(WillPush);
        mFindTimeDict[pStartNode] = mCurrTime++;

        while (Stk.Count > 0) {
            JyoutaiDef Peeked = Stk.Peek(); //PopでなくPeekを使う

            bool Pushed = false;
            foreach (int EachToNode in mToNodeArrDict[Peeked.CurrNode].OrderBy(pX => pX)) {
                if (mFindTimeDict.ContainsKey(EachToNode)) continue;

                mFindTimeDict[EachToNode] = mCurrTime++;

                WillPush.CurrNode = EachToNode;
                Stk.Push(WillPush);
                Pushed = true;
                break; // 子ノードを1つPushしたらBreak
            }

            if (Pushed == false) {
                mEndTimeDict[Peeked.CurrNode] = mCurrTime++;
                Stk.Pop(); // スタックのTopを消しておく
            }
        }
    }
}

解説

再帰を使わずに、While文を使ってますが
再帰を使うほうがシンプルに書けます。