AIMTech Round3 D1B Recover the String

これもいい問題だなぁ

問題概要(原文)

バイナリ文字列から全ての部分列を取ったときに $\{ 0,\;0 \}, \{ 0,\;1 \}, \{ 1,\;0 \}, \{ 1,\;1 \}$ の数が与えられる. 条件を満たす文字列があるならば一例を示せ.

考察

$\{ 0,\;0 \}, \{ 1,\;1 \}$ の数は組合せで試せる. $\{ 1,\;0 \}$ を転倒数だと思って処理する.残りは必ず $\{ 0,\;1 \}$ と一致するはず.

組合せが $0$ 通りになるのは $0,1$ 個の $2$ 通りの場合があり,空文字列が許されないことに注意せよ.

ソースコード

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Collections.Generic;
using Debug = System.Diagnostics.Debug;
using StringBuilder = System.Text.StringBuilder;
using System.Numerics;
using Number = System.Int64;
namespace Program
{
    public class Solver
    {
        public void Solve()
        {
            var a = sc.Long(4);
            var A = new List<long>();
            var B = new List<long>();
            for (long i = 0; i < 100000; i++)
            {
                if (i * (i - 1) / 2 == a[0]) A.Add(i);
                if (i * (i - 1) / 2 == a[3]) B.Add(i);
            }
            foreach (var x in A)
                foreach (var y in B)
                {
                    var s = get(x, y, a[1], a[2]);
                    if (!string.IsNullOrEmpty(s))
                    {
                        IO.Printer.Out.WriteLine(s);
                        return;
                    }

                }
            IO.Printer.Out.WriteLine("Impossible");
        }
        string get(long x, long y, long u, long v)
        {
            var sb = new List<int>();
            for (int i = 0; i < y; i++)
            {
                var rem = y - i;
                var k = v / rem;
                if (k > x) return null;
                x -= k;
                v -= rem * k;
                u -= i * k;
                for (int j = 0; j < k; j++)
                    sb.Add(0);
                sb.Add(1);
            }
            u -= y * x;
            for (int i = 0; i < x; i++)
                sb.Add(0);
            if (v != 0 || u != 0) return null;
            sb.Reverse();
            return sb.AsJoinedString("");
        }
        public IO.StreamScanner sc = new IO.StreamScanner(Console.OpenStandardInput());
        static T[] Enumerate<T>(int n, Func<int, T> f) { var a = new T[n]; for (int i = 0; i < n; ++i) a[i] = f(i); return a; }
        static public void Swap<T>(ref T a, ref T b) { var tmp = a; a = b; b = tmp; }


    }
}
#region main
static class Ex
{
    static public string AsString(this IEnumerable<char> ie) { return new string(System.Linq.Enumerable.ToArray(ie)); }
    static public string AsJoinedString<T>(this IEnumerable<T> ie, string st = " ") { return string.Join(st, ie); }
    static public void Main()
    {
        var solver = new Program.Solver();
        solver.Solve();
        Program.IO.Printer.Out.Flush();
    }
}
#endregion
#region Ex
namespace Program.IO
{
    using System.IO;
    using System.Text;
    using System.Globalization;
    public class Printer: StreamWriter
    {
        static Printer() { Out = new Printer(Console.OpenStandardOutput()) { AutoFlush = false }; }
        public static Printer Out { get; set; }
        public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } }
        public Printer(System.IO.Stream stream) : base(stream, new UTF8Encoding(false, true)) { }
        public Printer(System.IO.Stream stream, Encoding encoding) : base(stream, encoding) { }
        public void Write<T>(string format, T[] source) { base.Write(format, source.OfType<object>().ToArray()); }
        public void WriteLine<T>(string format, T[] source) { base.WriteLine(format, source.OfType<object>().ToArray()); }
    }
    public class StreamScanner
    {
        public StreamScanner(Stream stream) { str = stream; }
        public readonly Stream str;
        private readonly byte[] buf = new byte[1024];
        private int len, ptr;
        public bool isEof = false;
        public bool IsEndOfStream { get { return isEof; } }
        private byte read()
        {
            if (isEof) return 0;
            if (ptr >= len) { ptr = 0; if ((len = str.Read(buf, 0, 1024)) <= 0) { isEof = true; return 0; } }
            return buf[ptr++];
        }
        public char Char() { byte b = 0; do b = read(); while ((b < 33 || 126 < b) && !isEof); return (char)b; }

        public string Scan()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b >= 33 && b <= 126; b = (char)read())
                sb.Append(b);
            return sb.ToString();
        }
        public string ScanLine()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b != '\n'; b = (char)read())
                if (b == 0) break;
                else if (b != '\r') sb.Append(b);
            return sb.ToString();
        }
        public long Long()
        {
            if (isEof) return long.MinValue;
            long ret = 0; byte b = 0; var ng = false;
            do b = read();
            while (b != 0 && b != '-' && (b < '0' || '9' < b));
            if (b == 0) return long.MinValue;
            if (b == '-') { ng = true; b = read(); }
            for (; true; b = read())
            {
                if (b < '0' || '9' < b)
                    return ng ? -ret : ret;
                else ret = ret * 10 + b - '0';
            }
        }
        public int Integer() { return (isEof) ? int.MinValue : (int)Long(); }
        public double Double() { var s = Scan(); return s != "" ? double.Parse(s, CultureInfo.InvariantCulture) : double.NaN; }
        private T[] enumerate<T>(int n, Func<T> f)
        {
            var a = new T[n];
            for (int i = 0; i < n; ++i) a[i] = f();
            return a;
        }

        public char[] Char(int n) { return enumerate(n, Char); }
        public string[] Scan(int n) { return enumerate(n, Scan); }
        public double[] Double(int n) { return enumerate(n, Double); }
        public int[] Integer(int n) { return enumerate(n, Integer); }
        public long[] Long(int n) { return enumerate(n, Long); }
    }
}
#endregion


コメント

  • 空文字列の罠にハマった