Merge pull request #189 from anmol-tripathi83/master

Added Valid Sudoko problem #175

Java/Valid_Sudoko_problem/problem.md

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+Link to the problem statement: https://leetcode.com/problems/valid-sudoku/description/
+
+
+Problem Statement: Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:
+
+Each row must contain the digits 1-9 without repetition.
+Each column must contain the digits 1-9 without repetition.
+Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition.
+Note:
+
+A Sudoku board (partially filled) could be valid but is not necessarily solvable.
+Only the filled cells need to be validated according to the mentioned rules.
+
+
+Example 1:
+Input: board = 
+[["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"]]
+Output: true
+
+Example 2:
+Input: board = 
+[["8","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"]]
+Output: false
+Explanation: Same as Example 1, except with the 5 in the top left corner being modified to 8. Since there are two 8's in the top left 3x3 sub-box, it is invalid.

Java/Valid_Sudoko_problem/solution.java

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+// Collect the set of things we see, encoded as strings. For example:
+
+// '4' in row 7 is encoded as "(4)7".
+// '4' in column 7 is encoded as "7(4)".
+// '4' in the top-right block is encoded as "0(4)2".
+// Scream false if we ever fail to add something because it was already added (i.e., seen before).
+
+import java.util.*;
+
+class solution{
+    public static void main(String[] args) {
+        char[][] board = {{'5','3','.','.','7','.','.','.','.'}
+        ,{'6','.','.','1','9','5','.','.','.'}
+        ,{'.','9','8','.','.','.','.','6','.'}
+        ,{'8','.','.','.','6','.','.','.','.'}
+        ,{'4','.','.','8','.','3','.','.','1'}
+        ,{'7','.','.','.','2','.','.','.','6'}
+        ,{'.','6','.','.','.','.','2','8','.'}
+        ,{'.','.','.','4','1','9','.','.','5'}
+        ,{'.','.','.','.','8','.','.','7','9'}};
+
+        System.out.println(isValidSudoko(board));
+    }
+    public static boolean isValidSudoko(char[][] board) {
+        Set seen = new HashSet();
+        for (int i=0; i<9; ++i) {
+            for (int j=0; j<9; ++j) {
+                if (board[i][j] != '.') {
+                    String b = "(" + board[i][j] + ")";
+                    if (!seen.add(b + i) || !seen.add(j + b) || !seen.add(i/3 + b + j/3));
+                        return false;
+                }
+            }
+        }
+        return true;
+    }
+}