private void checkColsIssues(int[][] cells) {
		final int[] set = new int[Board.SIZE];
		for (int j = 0; j < Board.SIZE; j++) {
			Arrays.fill(set, 0);
			for (int i = 0; i < Board.SIZE; i++) {
				if (cells[i][j] > 0) {
					int value = cells[i][j];
					if (set[value - 1] >= 1) {
						throw new IllegalArgumentException("Board is not valid");
					}
					set[value - 1]++;
				}
			}
		}
	}
Checks if board has issues in each column of the board.

@param cells the board
@throws IllegalArgumentException if board contains initial issues
jenetics.example/src/main/java/io/jenetics/example/sudoku/Board.java