"Number of Islands"

Author: lennylxx

Diff for: README.md

@@ -11,6 +11,7 @@ them with C++ Language.
 
 |     | Problem                                                      | Solution           |
 | --- | ------------------------------------------------------------ | ------------------ |
+| 200 | [Number of Islands]                                          | [C](src/200.c)     |
 | 199 | [Binary Tree Right Side View]                                | [C](src/199.c)     |
 | 198 | [House Robber]                                               | [C](src/198.c)     |
 | 191 | [Number of 1 Bits]                                           | [C](src/191.c)     |
@@ -198,6 +199,8 @@ them with C++ Language.
 
 [LeetCode algorithm problems]: https://leetcode.com/problemset/algorithms/
 
+
+[Number of Islands]: https://leetcode.com/problems/number-of-islands/
 [Binary Tree Right Side View]: https://leetcode.com/problems/binary-tree-right-side-view/
 [House Robber]: https://leetcode.com/problems/house-robber/
 [Number of 1 Bits]: https://leetcode.com/problems/number-of-1-bits/

Diff for: src/200.c

@@ -0,0 +1,54 @@
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+void dfs(char **grid, bool **visited, int i, int j, int numRows, int numColumns) {
+    if (i >= 0 && i < numRows && j >= 0 && j < numColumns && !visited[i][j]) {
+        visited[i][j] = 1;
+        if (grid[i][j] == '1') { /* island */
+            dfs(grid, visited, i, j - 1, numRows, numColumns); /* left */
+            dfs(grid, visited, i, j + 1, numRows, numColumns); /* right */
+            dfs(grid, visited, i - 1, j, numRows, numColumns); /* up */
+            dfs(grid, visited, i + 1, j, numRows, numColumns); /* down */
+        }
+    }
+}
+
+int numIslands(char **grid, int numRows, int numColumns) {
+    if (grid == NULL || numRows == 0 || strlen(grid[0]) == 0)
+        return 0;
+
+    int i, j;
+    int count = 0;
+
+    bool **visited = (bool **)calloc(numRows, sizeof(bool *));
+    for (i = 0; i < numRows; i++) {
+        visited[i] = (bool *)calloc(numColumns, sizeof(bool));
+    }
+
+    for (i = 0; i < numRows; i++) {
+        for (j = 0; j < numColumns; j++) {
+            if (!visited[i][j]) { /* has not been visited */
+                if (grid[i][j] == '1') /* it's an island */
+                    count++;
+                dfs(grid, visited, i, j, numRows, numColumns);
+            }
+        }
+    }
+    return count;
+}
+
+int main() {
+    int row = 3;
+    int col = 3;
+    char **grid = (char **)calloc(1, sizeof(char *));
+
+    grid[0] = "111";
+    grid[1] = "010";
+    grid[2] = "111";
+
+    /* should be 1 */
+    printf("%d\n", numIslands(grid, row, col));
+    return 0;
+}