Paiza_Lerning_search-island.cs

//島探し (paizaランク S 相当)
//https://paiza.jp/learning/search-island

using System;
using System.Collections.Generic;

public class Program {

    public static void Main() {
        var s = Console.ReadLine().Split( ' ' );
        var mx = int.Parse( s[0] ); //列数
        var my = int.Parse( s[1] ); //行数
        var map = new bool[mx, my];

        for( var y = 0; y < my; y++ ) {
            var line = Console.ReadLine();
            if( string.IsNullOrWhiteSpace( line ) )
                break;
            s = line.Split( ' ' );
            for( var x = 0; x < mx && x <= s.Length; x++ ) {
                map[x, y] = "1".Equals( s[x] );
            }
        }

        var islands = 0;

        for( var y = 0; y < my; y++ ) {
            for( var x = 0; x < mx; x++ ) {
                if( map[x, y] ) {
                    islands++;
                    checkRounds( map, x, y );
                }
            }
        }

        Console.WriteLine( islands );
    }

    private struct Point {
        public Point( int x, int y ) {
            this.X = x;
            this.Y = y;
        }

        public readonly int X;
        public readonly int Y;
    }

    private static void checkRounds( bool[,] map, int x, int y ) {
        var queue = new Queue<Point>();
        var mx = map.GetLength( 0 );
        var my = map.GetLength( 1 );

        queue.Enqueue( new Point( x, y ) );
        map[x, y] = false;

        while( 0 < queue.Count ) {
            var p = queue.Dequeue();

            //left
            if( 0 < p.X && map[p.X - 1, p.Y] ) {
                queue.Enqueue( new Point( p.X - 1, p.Y ) );
                map[p.X - 1, p.Y] = false;
            }
            //right
            if( p.X < mx - 1 && map[p.X + 1, p.Y] ) {
                queue.Enqueue( new Point( p.X + 1, p.Y ) );
                map[p.X + 1, p.Y] = false;
            }
            //up
            if( 0 < p.Y && map[p.X, p.Y - 1] ) {
                queue.Enqueue( new Point( p.X, p.Y - 1 ) );
                map[p.X, p.Y - 1] = false;
            }
            //down
            if( p.Y < my - 1 && map[p.X, p.Y + 1] ) {
                queue.Enqueue( new Point( p.X, p.Y + 1 ) );
                map[p.X, p.Y + 1] = false;
            }
        }
    }
}