Paiza_Lerning_long-table.cs

//Paiza Lerning 長テーブルのうなぎ屋 (paizaランク B 相当)
//https://paiza.jp/learning/long-table

using System;
using System.Collections.Generic;

public class Program {

    public static void Main() {
        var s = Console.ReadLine().Split( ' ' );
        var chairCount = int.Parse( s[0] ); //座席数
        var groupCount = int.Parse( s[1] ); //グループ数
        var chairs = new bool[chairCount];

        while( 0 < groupCount ) {
            groupCount -= 1;
            s = Console.ReadLine().Split( ' ' );
            var personCount = int.Parse( s[0] );    //グループ人数
            var startPos = int.Parse( s[1] ) - 1;   //着席開始位置

            var canSit = true;
            for( var i = 0; i < personCount; i++ ) {
                var p = startPos + i;
                if( chairCount - 1 < p ) {
                    p -= chairCount;
                }

                if( chairs[p] ) {
                    canSit = false;
                    break;
                }
            }

            if( canSit ) {
                for( var i = 0; i < personCount; i++ ) {
                    var p = startPos + i;
                    if( chairCount - 1 < p ) {
                        p -= chairCount;
                    }
                    chairs[p] = true;
                }
            }
        }

        var count = 0;
        for( var i = 0; i < chairCount; i++ ) {
            if( chairs[i] )
                count += 1;
        }

        Console.WriteLine( count );
    }
}