Add number of islands solution

Author: hyunjung-choi

number-of-islands/hyunjung-choi.kt

@@ -0,0 +1,38 @@
+/**
+ * 시간복잡도: O(M × N)
+ * 공간복잡도: O(M × N)
+ */
+
+class Solution {
+    fun numIslands(grid: Array<CharArray>): Int {
+        if (grid.isEmpty() || grid[0].isEmpty()) return 0
+
+        val row = grid.size
+        val column = grid[0].size
+        var isIslandCount = 0
+
+        for (i in 0 until row) {
+            for (j in 0 until column) {
+                if (grid[i][j] == '1') {
+                    isIslandCount++
+                    dfs(grid, i, j, row, column)
+                }
+            }
+        }
+
+        return isIslandCount
+    }
+
+    private fun dfs(grid: Array<CharArray>, i: Int, j: Int, row: Int, column: Int) {
+        if (i < 0 || i >= row || j < 0 || j >= column || grid[i][j] != '1') {
+            return
+        }
+
+        grid[i][j] = '0'
+
+        dfs(grid, i - 1, j, row, column)
+        dfs(grid, i + 1, j, row, column)
+        dfs(grid, i, j - 1, row, column)
+        dfs(grid, i, j + 1, row, column)
+    }
+}