validation

SudokuBacktracking.groovy

    private boolean isValid() {
        boolean right = true
        board.each { row ->
            if (row.findAll { it != 0 }.countBy { it }.any { k, v -> v != 1 }) {
                right = false
            }
        }
        (0..this.board.size() - 1).each { colNum ->
            List<Integer> column = board.collect { it[colNum] }
            if (column.findAll { it != 0 }.countBy { it }.any { k, v -> v != 1 }) {
                right = false
            }
        }

        Map<String, List<Integer>> squares = [:]
        board.eachWithIndex { List<Integer> row, int i ->
            row.eachWithIndex { int entry, int j ->
                String key = findSquare(i, j)
                if (!squares.containsKey(key)) {
                    squares[key] = [entry]
                } else {
                    squares[key] << entry
                }
            }
        }

        squares.values().each { square ->
            if (square.findAll { it != 0 }.countBy { it }.any { k, v -> v != 1 }) {
                right = false
            }
        }
        return right
    }

    private String findSquare(int i, int j) {
        int squareCount = Math.sqrt(board.size()) as Integer
        return "${Math.floor(i / squareCount)}${Math.floor(j / squareCount)}".toString()
    }