A24 LIS

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

    static void Main()
    {
        List<string> InputList = GetInputList();
        int[] AArr = InputList[1].Split(' ').Select(pX => int.Parse(pX)).ToArray();
        Console.WriteLine(DeriveLISLen(AArr));
    }

    // 列挙を引数として、LISの長さを返す
    static int DeriveLISLen(IEnumerable<int> pEnum)
    {
        // LISの最終値の最小値[LISの長さ] なDP表
        var DPSortedList = new SortedList<int, int>();

        foreach (int EachA in pEnum) {
            if (DPSortedList.Count == 0) {
                DPSortedList[1] = EachA;
                continue;
            }
            int UpsertKeyInd = ExecNibunhou(DPSortedList, EachA);

            int CurrUB = DPSortedList.Count - 1;
            var Keys = DPSortedList.Keys;

            // 更新する位置によって分岐
            if (UpsertKeyInd <= CurrUB) {
                DPSortedList[Keys[UpsertKeyInd]] = EachA;
            }
            else {
                int PrevKey = Keys[CurrUB];
                DPSortedList[PrevKey + 1] = EachA;
            }
        }

        return DPSortedList.Keys.Max();
    }

    // 二分法で、引数の値を設定する、キーの配列の添字を返す
    static int ExecNibunhou(SortedList<int, int> pDPSortedList, int pTargetVal)
    {
        int UB = pDPSortedList.Count - 1;
        var Keys = pDPSortedList.Keys;

        // 最小値以下の場合
        if (pTargetVal <= pDPSortedList[Keys[0]]) {
            return 0;
        }

        // 最大値より大きい場合
        if (pTargetVal > pDPSortedList[Keys[UB]]) {
            return UB + 1;
        }

        int L = 0;
        int R = UB;

        while (L + 1 < R) {
            int Mid = (L + R) / 2;
            if (pDPSortedList[Keys[Mid]] < pTargetVal) {
                L = Mid;
            }
            else {
                R = Mid;
            }
        }
        return R;
    }
}

解説

LISの長さを求めてます。