feat: add Word Search LeetCode problem (#1160)

Co-authored-by: David Leal <halfpacho@gmail.com>

leetcode/DIRECTORY.md

@@ -31,6 +31,7 @@
 | 53   | [Maximum Subarray](https://leetcode.com/problems/maximum-subarray/)                                                             | [C](./src/53.c)   | Easy       |
 | 62   | [Unique Paths](https://leetcode.com/problems/unique-paths/description/)                                                         | [C](./src/62.c)   | Medium     |
 | 66   | [Plus One](https://leetcode.com/problems/plus-one/)                                                                             | [C](./src/66.c)   | Easy       |
+| 79   | [Word Search](https://leetcode.com/problems/word-search/)                                                                       | [C](./src/79.c)   | Medium     |
 | 82   | [Remove Duplicates from Sorted List II](https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/)                   | [C](./src/82.c)   | Medium     |
 | 83   | [Remove Duplicates from Sorted List](https://leetcode.com/problems/remove-duplicates-from-sorted-list/)                         | [C](./src/83.c)   | Easy       |
 | 94   | [Binary Tree Inorder Traversal](https://leetcode.com/problems/binary-tree-inorder-traversal/)                                   | [C](./src/94.c)   | Medium     |

leetcode/src/79.c

@@ -0,0 +1,60 @@
+int getPointKey(int i, int j, int boardSize, int boardColSize){
+    return boardSize * boardColSize * i + j;
+}
+
+const int directionsSize = 4;
+const int directions[4][2] = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
+
+bool exitsWord(int i, int j, char** board, int boardSize, int* boardColSize, int wordIndex, char* word, int* vistedPointSet){
+    if (board[i][j] != word[wordIndex]){
+        return false;
+    }
+    
+    if (wordIndex == strlen(word) - 1){
+        return true;
+    }
+    
+    for (int k = 0; k < directionsSize; k++){
+        int nextI = i + directions[k][0];
+        int nextJ = j + directions[k][1];
+        
+        if (nextI < 0 || nextI >= boardSize || nextJ < 0 || nextJ >= boardColSize[i]){
+            continue;
+        }
+        
+        int key = getPointKey(nextI, nextJ, boardSize, boardColSize[i]);
+        if (vistedPointSet[key] == 1){
+            continue;
+        }
+        
+        vistedPointSet[key] = 1;
+        if (exitsWord(nextI, nextJ, board, boardSize, boardColSize, wordIndex + 1, word, vistedPointSet)){
+            return true;
+        }
+
+        vistedPointSet[key] = 0;
+    }
+    
+    return false;
+}
+
+
+// Use backtracking.
+// Runtime: Runtime: O(n*m*4^len(word))
+bool exist(char** board, int boardSize, int* boardColSize, char* word){
+    int* vistedPointSet = (int*) calloc(getPointKey(boardSize, boardColSize[0], boardSize, boardColSize[0]), sizeof(int));
+
+    for (int i = 0; i < boardSize; i++){
+        for (int j = 0; j < boardColSize[i]; j++){
+            int key = getPointKey(i, j, boardSize, boardColSize[i]);
+            vistedPointSet[key] = 1;
+            if (exitsWord(i, j, board, boardSize, boardColSize, 0, word, vistedPointSet)){
+                return true;
+            };
+            
+            vistedPointSet[key] = 0;
+        }
+    }
+    
+    return false;
+}