250316 스도쿠

public static void main(String[] args) throws IOException {
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	int[][] board = new int[9][9];

	for (int i = 0; i < 9; i++) {
		char[] row = br.readLine().toCharArray();
		for (int j = 0; j < 9; j++) {
			board[i][j] = row[j] - '0';
		}
	}

	dfs(board, 0);

	StringBuilder sb = new StringBuilder();
	for (int[] row : board) {
		for (int num : row) {
			sb.append(num);
		}
		sb.append("\n");
	}
	System.out.print(sb);
}

private static boolean dfs(int[][] board, int depth) {
	if (depth == 81) {
		return true;
	}

	int row = depth / 9;
	int col = depth % 9;

	if (board[row][col] != 0) {
		return dfs(board, depth + 1);
	}

	for (int num = 1; num <= 9; num++) {
		if (isValid(board, row, col, num)) {
			board[row][col] = num;
			if (dfs(board, depth + 1)) {
				return true;
			}
			board[row][col] = 0;
		}
	}

	return false;
}

private static boolean isValid(int[][] board, int row, int col, int num) {
	for (int i = 0; i < 9; i++) {
		if (board[i][col] == num || board[row][i] == num) {
			return false;
		}
	}

	int startRow = (row / 3) * 3;
	int startCol = (col / 3) * 3;
	for (int i = 0; i < 3; i++) {
		for (int j = 0; j < 3; j++) {
			if (board[startRow + i][startCol + j] == num) {
				return false;
			}
		}
	}

	return true;
}

출처:https://www.acmicpc.net/problem/2239