Add bfs count islands (#612)

* [Add] Create count_islands.py

Add count_islands problem in bfs section.

* [Edit] Add description in count_islands problem

Add description in count_islands problem in bfs section.

* [Edit] Add examples in count_islands problem

Add two examples in count_islands problem in bfs section.

* [Edit] Add counting_islands method

Add counting_islands method in count_islands.py in bfs section.

* [Edit] Modify count_islands problem in bfs

Add needed variables.

* [Edit] Implement counting_islands method

Complete counting_islands method.

* [Edit] Add examples

Add test cases and testing code.

* [Edit] Delete testing code

* [Edit] Change method's name

Change counting_islands to count_islands in count_islands problem.

* [Edit] Add unittest

Implement unittest func. of count_islands problem in bfs section.

* [Edit] Edit count_islands method

While func. is shortened.

* [Delete] Delete unittest of count_islands problem

This reverts commit 8cd0a66.

* [Edit] Add unittest

Implement unittest func. of count_islands problem and edit init file.

Author: guswh11

algorithms/bfs/__init__.py

@@ -1,3 +1,4 @@
+from .count_islands import *
 from .maze_search import *
 from .shortest_distance_from_all_buildings import *
 from .word_ladder import *

algorithms/bfs/count_islands.py

@@ -0,0 +1,65 @@
+"""
+This is a bfs-version of counting-islands problem in dfs section.
+Given a 2d grid map of '1's (land) and '0's (water),
+count the number of islands.
+An island is surrounded by water and is formed by
+connecting adjacent lands horizontally or vertically.
+You may assume all four edges of the grid are all surrounded by water.
+
+Example 1:
+11110
+11010
+11000
+00000
+Answer: 1
+
+Example 2:
+11000
+11000
+00100
+00011
+Answer: 3
+
+Example 3:
+111000
+110000
+100001
+001101
+001100
+Answer: 3
+
+Example 4:
+110011
+001100
+000001
+111100
+Answer: 5
+"""
+
+
+def count_islands(grid):
+    row = len(grid)
+    col = len(grid[0])
+
+    num_islands = 0
+    visited = [[0] * col for i in range(row)]
+    directions = [[-1, 0], [1, 0], [0, -1], [0, 1]]
+    queue = []
+
+    for i in range(row):
+        for j, num in enumerate(grid[i]):
+            if num == 1 and visited[i][j] != 1:
+                visited[i][j] = 1
+                queue.append((i, j))
+                while queue:
+                    x, y = queue.pop(0)
+                    for k in range(len(directions)):
+                        nx_x = x + directions[k][0]
+                        nx_y = y + directions[k][1]
+                        if nx_x >= 0 and nx_y >= 0 and nx_x < row and nx_y < col:
+                            if visited[nx_x][nx_y] != 1 and grid[nx_x][nx_y] == 1:
+                                queue.append((nx_x, nx_y))
+                                visited[nx_x][nx_y] = 1
+                num_islands += 1
+
+    return num_islands

tests/test_bfs.py

@@ -1,4 +1,5 @@
 from algorithms.bfs import (
+    count_islands,
     maze_search,
     shortest_distance_from_all_buildings,
     ladder_length
@@ -7,8 +8,21 @@
 import unittest
 
 
+class TestCountIslands(unittest.TestCase):
+
+    def test_count_islands(self):
+        grid_1 = [[1,1,1,1,0], [1,1,0,1,0], [1,1,0,0,0], [0,0,0,0,0]]
+        self.assertEqual(1, count_islands(grid_1))
+        grid_2 = [[1,1,0,0,0], [1,1,0,0,0], [0,0,1,0,0], [0,0,0,1,1]]
+        self.assertEqual(3, count_islands(grid_2))
+        grid_3 = [[1,1,1,0,0,0], [1,1,0,0,0,0], [1,0,0,0,0,1], [0,0,1,1,0,1], [0,0,1,1,0,0]]
+        self.assertEqual(3, count_islands(grid_3))
+        grid_4 = [[1,1,0,0,1,1], [0,0,1,1,0,0], [0,0,0,0,0,1], [1,1,1,1,0,0]]
+        self.assertEqual(5, count_islands(grid_4))
+
+
 class TestMazeSearch(unittest.TestCase):
-    
+
     def test_maze_search(self):
         grid_1 = [[1,0,1,1,1,1],[1,0,1,0,1,0],[1,0,1,0,1,1],[1,1,1,0,1,1]]
         self.assertEqual(14, maze_search(grid_1))