Added a Leetcode solution for Valid Sudoku (#134)

Author: SauravP97

Diff for: Java/valid-sudoku.java

@@ -0,0 +1,76 @@
+/** 
+ *  Problem Name : Valid Sudoku
+ *  Concept Involved : 2D Array, Frequency Count
+ * 
+ *  Execution Time : 2 ms
+ *  Memory Consumed : 38.8 mb
+ * 
+ *  Solution : We have been given with a Sudoku
+ *  Puzzle, we have to determine whether the puzzle
+ *  is valid or not.
+ *  In order to check the validity every row and column
+ *  of sudoku must have numbers from 0 to 9 and in a non
+ *  repeating fashion and same for in every 3x3 block.
+ *  I have used array based indexing to compute the 
+ *  frequency of elements in every rows, columns and blocks
+ *  and checking its validity afterwards.
+ *  If every check is passed then we return True at the end.
+*/
+class Solution {
+    public boolean isValid(ArrayList<Integer> arr){
+        int[] fre = new int[10];
+        for(int ele : arr){
+            fre[ele]++;
+            if(fre[ele] > 1){
+                return false;
+            }
+        }
+        return true;
+    }
+    public boolean isValidSudoku(char[][] board) {
+        for(int i=0; i<9; i++){
+            ArrayList<Integer> row = new ArrayList<>();
+            for(int j=0; j<9; j++){
+                if(board[i][j] != '.'){
+                    int num = board[i][j] - '0';
+                    row.add(num);
+                }
+            }
+            if(!isValid(row)){
+                return false;
+            }
+        }
+        
+        for(int i=0; i<9; i++){
+            ArrayList<Integer> col = new ArrayList<>();
+            for(int j=0; j<9; j++){
+                if(board[j][i] != '.'){
+                    int num = board[j][i] - '0';
+                    col.add(num);
+                }
+            }
+            if(!isValid(col)){
+                return false;
+            }
+        }
+        
+        for(int i=0; i<9; i+=3){
+            for(int j=0; j<9; j+=3){
+                ArrayList<Integer> block = new ArrayList<>();
+                for(int k=i;k<i+3;k++){
+                    for(int l=j;l<j+3;l++){
+                        if(board[k][l] != '.'){
+                            int num = board[k][l] - '0';
+                            block.add(num);
+                        }
+                    }
+                }
+                if(!isValid(block)){
+                    return false;
+                }
+            }
+        }
+        
+        return true;
+    }
+}

Diff for: README.md

@@ -139,6 +139,7 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | 124  | [Permutation by Recussion](https://leetcode.com/problems/permutations/)                                                          | [Java](./Java/shuffle-the-array.java)                                                                             | O(N)         | O(N)          | Easy       | Array              |
 | 283     | [Move-Zeroes](https://leetcode.com/problems/move-zeroes/)                                                                     | [C++](./C++/Move-Zeroes.cpp)                                                                                      | O(N)         | O(1)          | Easy       | Array              |
 | 27     | [Remove-Element](https://leetcode.com/problems/remove-element/)                                                                     | [C++](./C++/remove-element.cpp)                                                                                      | O(N)         | O(1)          | Easy       | Array              |
+| 36     | [Valid Sudoku](https://leetcode.com/problems/valid-sudoku/)                                                                     | [Java](./Java/valid-sudoku.java)                                                                                      | O(N^2)         | O(N)          | Medium       | Array, 2D Matrix              |
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