ROITI Pyramid O(n^2)

import java.util.Scanner;

class Pyramid{

    public static void Build(int N){
        int width = (int)(-1+Math.sqrt(1-(-4*2*N)))/2;
        int number = 0;

        if((width*(width+1)/2)<N){
            width++;
        }

        StringBuilder spaces = new StringBuilder();
        // concatenation O(n^2) and loop becomes O(n^3)

        for (int i = 1; i <= width; i++) {
            spaces.setLength(0);
            for (int j = 0; j < width-i; j++) {
                spaces.append(" ");
            }
            System.out.print(spaces);
            for (int c = 0; c < i; c++) {
                if(number>=N)break;
                System.out.print(++number + " ");
            }
            System.out.print(spaces);

        System.out.println();
        }
    }

    public static void main(String[] args){
        Scanner scanner = new Scanner(System.in);
        System.out.println("Please, input N: ");
        int N = scanner.nextInt();
        Build(N);
        scanner.close();
    }
}