Problem:
Score : 200 points

Problem Statement

There is a grid of squares with H horizontal rows and W vertical columns.
The square at the i-th row from the top and the j-th column from the left is represented as (i, j).
Each square is black or white.
The color of the square is given as an H-by-W matrix (a_{i, j}).
If a_{i, j} is ., the square (i, j) is white; if a_{i, j} is #, the square (i, j) is black.

Snuke is compressing this grid.
He will do so by repeatedly performing the following operation while there is a row or column that consists only of white squares:

Operation: choose any one row or column that consists only of white squares, remove it and delete the space between the rows or columns.

It can be shown that the final state of the grid is uniquely determined regardless of what row or column is chosen in each operation.
Find the final state of the grid.

Constraints

1 \leq H, W \leq 100

a_{i, j} is . or #.

There is at least one black square in the whole grid.

Input

Input is given from Standard Input in the following format:

H W
a_{1, 1}...a_{1, W}
:
a_{H, 1}...a_{H, W}

Output

Print the final state of the grid in the same format as input (without the numbers of rows and columns); see the samples for clarity.

Sample Input 1

4 4
##.#
....
##.#
.#.#

Sample Output 1

###
###
.##

The second row and the third column in the original grid will be removed.

Sample Input 2

3 3
#..
.#.
..#

Sample Output 2

#..
.#.
..#

As there is no row or column that consists only of white squares, no operation will be performed.

Sample Input 3

4 5
.....
.....
..#..
.....

Sample Output 3

#

Sample Input 4

7 6
......
....#.
.#....
..#...
..#...
......
.#..#.

Sample Output 4

..#
#..
.#.
.#.
#.#

Solution in C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Buffers;
using System.Collections.Generic;
using System.IO;
using System.Runtime.CompilerServices;
using System.Text;
using static Scanner;

class Program
{
    static void Main(string[] args) {
        var writer = new StreamWriter(Console.OpenStandardOutput()) {AutoFlush = false};
        Console.SetOut(writer);
        Solve();
        Console.Out.Flush();
    }
    static void Solve() {
        int H = ScanInt(), W = ScanInt();
        var a = new List<string>();
        for (int i = 0; i < H; i++) {
            var isAllWhite = true;
            var line = Scan();
            for (int j = 0; j < W; j++) {
                if (line[j] == '.') continue;
                isAllWhite = false;
                break;
            }
            if (!isAllWhite) a.Add(line);
        }
        var span = a.AsSpan();
        for (int i = 0; i < W; i++) {
            var isAllWhite = true;
            foreach (var s in span) {
                if (s[i] == '.') continue;
                isAllWhite = false;
                break;
            }
            if (!isAllWhite) continue;
            for (int j = 0; j < span.Length; j++) {
                span[j] = new StringBuilder(span[j][..i]).Append(span[j][(i + 1)..]).ToString();
            }
            i--;
            W--;
        }
        foreach (var line in span) {
            Console.WriteLine(line);
        }
    }
}

public static class Scanner
{
    static readonly Stream stream = Console.OpenStandardInput();
    static readonly byte[] buffer = ArrayPool<byte>.Shared.Rent(1024);
    static int length, p;
    static bool isEof;
    private static byte ConsoleIn() {
        if (isEof) return 0;
        if (p < length) return buffer[p++];
        p = 0;
        if ((length = stream.Read(buffer, 0, 1024)) > 0) return buffer[p++];
        isEof = true;
        return 0;
    }
    public static char GetChar() {
        var by = ConsoleIn();
        while ((by < '!' || '~' < by) && !isEof) by = ConsoleIn();
        return (char) by;
    }
    public static string Scan() {
        var sb = new StringBuilder();
        for (var ch = GetChar(); '!' <= ch && ch <= '~'; ch = (char) ConsoleIn()) {
            sb.Append(ch);
        }
        return sb.ToString();
    }
    public static int ScanInt() {
        var temp = 0;
        for (var ch = GetChar(); '0' <= ch && ch <= '9'; ch = (char) ConsoleIn()) {
            temp = temp * 10 + ch - '0';
        }
        return temp;
    }
}

class DList<T>
{
    public T[] Items;
}

static class ListExtensions
{
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static Span<T> AsSpan<T>(this List<T> list) {
        return Unsafe.As<DList<T>>(list).Items.AsSpan(0, list.Count);
    }
}