Question.java

package Q17_23_Max_Black_Square;

import CtCILibrary.AssortedMethods;

public class Question {	
	public static Subsquare findSquareWithSize(int[][] matrix, int squareSize) {
		// On an edge of length N, there are (N - sz + 1) squares of length sz.
		int count = matrix.length - squareSize + 1; 
		
		// Iterate through all squares with side length square_size.
		for (int row = 0; row < count; row++) {
			for (int col = 0; col < count; col++) {
				if (isSquare(matrix, row, col, squareSize)) {
					return new Subsquare(row, col, squareSize);
				}
			}
		}
		return null;
	}
	
	public static Subsquare findSquare(int[][] matrix){
		assert(matrix.length > 0);
		for (int row = 0; row < matrix.length; row++){
			assert(matrix[row].length == matrix.length);
		}
		
		int N = matrix.length;
		
		for (int i = N; i >= 1; i--) {
			Subsquare square = findSquareWithSize(matrix, i);
			if (square != null) {
				return square;
			}
		}
		return null;
	}	

	private static boolean isSquare(int[][] matrix, int row, int col, int size) {
		// Check top and bottom border.
		for (int j = 0; j < size; j++){
			if (matrix[row][col+j] == 1) {
				return false;
			}
			if (matrix[row+size-1][col+j] == 1) {
				return false;
			}
		}
		
		// Check left and right border.
		for (int i = 1; i < size - 1; i++) {
			if (matrix[row+i][col] == 1){
				return false;
			}
			if (matrix[row+i][col+size-1] == 1) {
				return false;
			}
		}
		return true;
	}
	
	public static void main(String[] args) {
		int[][] matrix = AssortedMethods.randomMatrix(7, 7, 0, 1);
		AssortedMethods.printMatrix(matrix);
		Subsquare square = findSquare(matrix);
		square.print();
	}
}