Here is my solution in java, time complexity O(n^2)`

public static void staircase(int n) {
    // Write your code here
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<n;j++)
        {   
            if(j<n-(i+1))
            System.out.print(" ");
            else
            System.out.print("#");
        }
        System.out.println();
    }
    }

function staircase(n) {
    
    let star = ""
    for (let i = 0; i < n ; i++) {
        
        for (let j = n - 1; j > i; j--) {
                star += " ";
        }

        for (let k = i; k >= 0; k--) {
            star += "#";
        }
        
        star += "\n";  
    }
    console.log(star)

}

def staircase(n):
    # Write your code here
    for i in range(n):
        print(" " * (n - i - 1) + "#" * (i + 1))

for(int i = 1; i <= n; i++) {
    char[] array = [..Enumerable.Repeat(' ', n-i), ..Enumerable.Repeat('#', i)];
    Console.WriteLine(array);
}

def staircase(n: int):
    for x in range(1, n + 1):
        print(" " * (n - x) + "#" * x)