Pretty easy with C#:

using System;
class Solution
{
    static void Main(String[] args)
    {
        int N = int.Parse(Console.ReadLine());
        for (int i = 0; i < N; i++)
            Console.WriteLine(new String('#', i + 1).PadLeft(N, ' '));
    }
}

Simple javascript solution

for (let i = 1; i <= n; i++) {
    console.log("#".repeat(i).padStart(n));
}

Love string arithmetic:

n = int(input())
for m in range(n):
    print((n - m - 1) * ' ' + (m + 1) * '#')

in Python3 :

def staircase(n):
    for i in range(1,n+1):
        print(' '*(n-i)+'#'*(i))

In Java I did this:

public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    int n = in.nextInt();
    char [] arreglo = new char [n];
    Arrays.fill(arreglo, ' ');
    int i = 0;
    for (i = 1; i <= n; i++){
        arreglo[n-i] = '#';
        System.out.println(arreglo);
    }

}

I hope it wasn't that bad XD but I wanted to post it cos I didn't find it that simple after all for Java. Made me think a lot. :)