solves word search

Author: anishLearnsToCode

README.md

@@ -72,6 +72,7 @@
 |  75  | [Sort Colors](https://leetcode.com/problems/sort-colors)                                                                                                  |                                                                   [![Java](assets/java.png)](src/SortColors.java)                                                                    |                                                                                                                                   |
 |  77  | [Combinations](https://leetcode.com/problems/combinations)                                                                                                |                                                                  [![Java](assets/java.png)](src/Combinations.java)                                                                   |                                                                                                                                   |
 |  78  | [Subsets](https://leetcode.com/problems/subsets)                                                                                                          |                                                                     [![Java](assets/java.png)](src/Subsets.java)                                                                     |                                                                                                                                   |
+|  79  | [Word Search](https://leetcode.com/problems/word-search)                                                                                                  |                                                                   [![Java](assets/java.png)](src/WordSearch.java)                                                                    |                                                                                                                                   |
 |  83  | [Remove Duplicates from Sorted List](https://leetcode.com/problems/remove-duplicates-from-sorted-list)                                                    |                   [![Java](assets/java.png)](src/RemoveDuplicatesFromSortedList.java) [![Python](assets/python.png)](python/remove_duplicates_from_linked_list.py)                   |                                                                                                                                   |
 |  88  | [Merge Sorted Array](https://leetcode.com/problems/merge-sorted-array)                                                                                    |                                  [![Java](assets/java.png)](src/MergeSortedArray.java) [![Python](assets/python.png)](python/merge_sorted_array.py)                                  |                                                                                                                                   |
 |  94  | [Binary Tree Inorder Traversal](https://leetcode.com/problems/binary-tree-inorder-traversal/)                                                             |                       [![Java](assets/java.png)](src/BinaryTreeInorderTraversal.java) [![Python](assets/python.png)](python/binary_tree_inorder_traversal.py)                        |                                                                                                                                   |

src/WordSearch.java

@@ -0,0 +1,35 @@
+// https://leetcode.com/problems/word-search
+// T: O(4^{m * n})
+// S: O(m * n)
+
+public class WordSearch {
+
+    public boolean exist(char[][] board, String word) {
+        final int rows = board.length, columns = board[0].length;
+
+        for (int row = 0; row < rows ; row++) {
+            for (int column = 0; column < columns ; column++) {
+                if (exist(board, row, column, word, 0)) {
+                    return true;
+                }
+            }
+        }
+
+        return false;
+    }
+
+    private boolean exist(char[][] board, int row, int column, String word, int i) {
+        if (i == word.length()) return true;
+        if (row < 0 || column < 0 || row == board.length || column == board[row].length) return false;
+        if (board[row][column] != word.charAt(i)) return false;
+
+        board[row][column] ^= 256;
+        boolean exist = exist(board, row, column+1, word, i + 1)
+                || exist(board, row, column - 1, word, i + 1)
+                || exist(board, row + 1, column, word, i + 1)
+                || exist(board, row - 1, column, word, i + 1);
+
+        board[row][column] ^= 256;
+        return exist;
+    }
+}