problems: add max area of island

problems/max-area-of-island.kt

@@ -0,0 +1,39 @@
+fun <A, B> product(xs: Sequence<A>, ys: Sequence<B>): Sequence<Pair<A, B>> =
+    xs.flatMap { x -> ys.map { y -> x to y } }
+
+fun <A, B> product(xs: Iterable<A>, ys: Iterable<B>): Sequence<Pair<A, B>> =
+    product(xs.asSequence(), ys.asSequence())
+    
+class Solution {
+    fun BFS(grid: Array<IntArray>, coords: Pair<Int, Int>): Int {
+        val queue = ArrayDeque<Pair<Int, Int>>()
+        queue.addLast(coords)
+
+        var size = 0
+        while (!queue.isEmpty()) {
+            val (y, x) = queue.removeFirst()
+            if (grid[y][x] != 1) {
+                continue
+            }
+            
+            for ((dy, dx) in sequenceOf(0 to 1, 1 to 0, 0 to -1, -1 to 0)) {
+                if (!(y + dy in grid.indices) || !(x + dx in grid[y + dy].indices)) {
+                    continue
+                } else if (grid[y + dy][x + dx] != 1) {
+                    continue
+                }
+
+                queue.addLast(y + dy to x + dx)
+            }
+            
+            // mark it as done
+            grid[y][x] = 0
+            size++
+        }
+        
+        return size
+    }
+    
+    fun maxAreaOfIsland(grid: Array<IntArray>): Int =
+        product(grid.indices, grid.first().indices).map { BFS(grid, it) }.max() ?: 0
+}