200

Author: TedTran2019

ruby/200-Number-of-Islands.rb

@@ -0,0 +1,29 @@
+DIRS = [[0, 1], [0, -1], [1, 0], [-1, 0]].freeze
+
+def num_islands(grid)
+  islands = 0
+  memo = Array.new(grid.length) { Array.new(grid[0].length) }
+  grid.each_with_index do |row, y|
+    row.each_with_index do |el, x|
+      if memo[y][x].nil? && el == '1'
+        islands += 1
+        flood_fill(grid, memo, y, x)
+      end
+    end
+  end
+  islands
+end
+
+def flood_fill(grid, memo, y, x)
+  return nil if y >= grid.length || y.negative? || 
+                x >= grid[0].length || x.negative? ||
+                memo[y][x] != nil ||
+                grid[y][x] == '0'
+
+  memo[y][x] = true
+  DIRS.each do |dy, dx|
+    dy += y
+    dx += x
+    flood_fill(grid, memo, dy, dx)
+  end
+end