Create 1905-count-sub-islands.java

This java translation follows the python solution as closely as possible. There are 2 changes which have been made to make the python solution work in java. The first change is that the class RecursiveBiFunction is defined. This class exists so that the dfs lambda expression may refer to itself. The second change is that the visit set contains flattened integer coordinates instead of tuples. This change is made because tuples do not exist in java, and using an int array would not provide the correct behavior as int arrays compare themselves by not by value, but by reference.

Author: AP-Repositories

java/1905-count-sub-islands.java

@@ -0,0 +1,42 @@
+class Solution {
+    class RecursiveBiFunction<A, B, C> {
+        BiFunction<A, B, C> func;
+    }
+    
+    public int countSubIslands(final int[][] grid1, final int[][] grid2) {
+        final int ROWS = grid1.length, COLS = grid1[0].length;
+        final Set<Integer> visit = new HashSet<>();
+        
+        final RecursiveBiFunction<Integer, Integer, Boolean> dfs = new RecursiveBiFunction<>();
+        dfs.func = (r, c) -> {
+            int flatCoord = r*COLS + c;
+            if(
+                r < 0 
+                || c < 0
+                || r == ROWS
+                || c == COLS
+                || grid2[r][c] == 0
+                || visit.contains(flatCoord)
+            )
+                return true;
+            
+            visit.add(flatCoord);
+            boolean res = true;
+            if(grid1[r][c] == 0)
+                res = false;
+            
+            res = dfs.func.apply(r - 1, c) && res;
+            res = dfs.func.apply(r + 1, c) && res;
+            res = dfs.func.apply(r, c - 1) && res;
+            res = dfs.func.apply(r, c + 1) && res;
+            return res;
+        };
+        
+        int count = 0;
+        for(int r = 0; r < ROWS; r++)
+            for(int c = 0; c < COLS; c++)
+                if(grid2[r][c] != 0 && !visit.contains(r*COLS + c) && dfs.func.apply(r, c))
+                    count += 1;
+        return count;
+    }
+}