Merge pull request codemistic#576 from namita27/patch-1

Checking if the given board is valid sudoku or not

Author: gantavyamalviya

Hashtable/Checking for a valid sudoku

@@ -0,0 +1,97 @@
+import java.util.*;
+
+class example2 {
+public static boolean notInRow(char arr[][], int row)
+{
+
+HashSet<Character> st = new HashSet<>();
+
+for (int i = 0; i < 9; i++) {
+if (st.contains(arr[row][i]))
+return false;
+
+if (arr[row][i] != '.')
+st.add(arr[row][i]);
+}
+return true;
+}
+
+public static boolean notInCol(char arr[][], int col)
+{
+HashSet<Character> st = new HashSet<>();
+
+for (int i = 0; i < 9; i++) {
+
+// If already encountered before,
+// return false
+if (st.contains(arr[i][col]))
+return false;
+
+// If it is not an empty cell,
+// insert value at the current
+// cell in the set
+if (arr[i][col] != '.')
+st.add(arr[i][col]);
+}
+return true;
+}
+
+public static boolean notInBox(char arr[][], int startRow, int startCol)
+{
+HashSet<Character> st = new HashSet<>();
+
+for (int row = 0; row < 3; row++) {
+for (int col = 0; col < 3; col++) {
+char curr = arr[row + startRow][col + startCol];
+ 
+if (st.contains(curr))
+return false;
+
+if (curr != '.')
+st.add(curr);
+}
+}
+return true;
+}
+public static boolean isValid(char arr[][], int row,
+int col)
+{
+return notInRow(arr, row) && notInCol(arr, col)
+&& notInBox(arr, row - row % 3, col - col % 3);
+}
+
+public static boolean isValidConfig(char arr[][], int n)
+{
+for (int i = 0; i < n; i++) {
+for (int j = 0; j < n; j++) {
+
+// If current row or current column or
+// current 3x3 box is not valid, return
+// false
+if (!isValid(arr, i, j))
+return false;
+}
+}
+return true;
+}
+
+public static void main(String[] args)
+{
+char[][] board = new char[][] {
+{ '5', '3', '.', '.', '7', '.', '.', '.', '.' },
+{ '6', '.', '.', '1', '9', '5', '.', '.', '.' },
+{ '.', '9', '8', '.', '.', '.', '.', '6', '.' },
+{ '8', '.', '.', '.', '6', '.', '.', '.', '3' },
+{ '4', '.', '.', '8', '.', '3', '.', '.', '1' },
+{ '7', '.', '.', '.', '2', '.', '.', '.', '6' },
+{ '.', '6', '.', '.', '.', '.', '2', '8', '.' },
+{ '.', '.', '.', '4', '1', '9', '.', '.', '5' },
+{ '.', '.', '.', '.', '8', '.', '.', '7', '9' }
+};
+
+// Function call
+System.out.println(
+(isValidConfig(board, 9) ? "YES" : "NO"));
+}
+}
+