ABC256-D Union of Interval

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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");
            WillReturn.Add("10 20");
            WillReturn.Add("20 30");
            WillReturn.Add("40 50");
            //10 30
            //40 50
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("3");
            WillReturn.Add("10 40");
            WillReturn.Add("30 60");
            WillReturn.Add("20 50");
            //10 60
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    struct RangeInfo
    {
        internal int RangeSta;
        internal int RangeEnd;
    }

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

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

        var RangeInfoList = new List<RangeInfo>();

        foreach (string EachStr in InputList.Skip(1)) {
            SplitAct(EachStr);

            RangeInfo WillAdd;
            WillAdd.RangeSta = wkArr[0];
            WillAdd.RangeEnd = wkArr[1];
            RangeInfoList.Add(WillAdd);
        }

        var Query = DeriveMergedRangeList(RangeInfoList);
        foreach (RangeInfo EachRangeInfo in Query) {
            Console.WriteLine("{0} {1}", EachRangeInfo.RangeSta, EachRangeInfo.RangeEnd);
        }
    }

    // 閉区間の列挙を引数として、
    // OverLapした閉区間をマージした列挙を返す
    static IEnumerable<RangeInfo> DeriveMergedRangeList(IEnumerable<RangeInfo> pRangeInfoEnum)
    {
        RangeInfo[] RangeInfoArr = pRangeInfoEnum.OrderBy(px => px.RangeSta).ToArray();

        int MergedRangeSta = RangeInfoArr[0].RangeSta;
        int MergedRangeEnd = RangeInfoArr[0].RangeEnd;

        int UB = RangeInfoArr.GetUpperBound(0);

        for (int I = 0; I <= UB; I++) {
            int CurrRangeSta = RangeInfoArr[I].RangeSta;
            int CurrRangeEnd = RangeInfoArr[I].RangeEnd;

            if (CurrRangeSta <= MergedRangeEnd && MergedRangeSta <= CurrRangeEnd) {
                // 今の区間とオーバーラップしてる場合
                MergedRangeEnd = Math.Max(MergedRangeEnd, CurrRangeEnd);
            }
            else {
                // 今の区間とオーバーラップしてない場合
                yield return new RangeInfo() { RangeSta = MergedRangeSta, RangeEnd = MergedRangeEnd };

                MergedRangeSta = CurrRangeSta;
                MergedRangeEnd = CurrRangeEnd;
            }

            if (I == UB) {
                yield return new RangeInfo() { RangeSta = MergedRangeSta, RangeEnd = MergedRangeEnd };
            }
        }
    }
}

解説

区間をStaの昇順にソートしてから
順に区間を見てます。