Assignment 4 open for review.

assignment4_solution.py

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+##################### Solution explanation ##########################################
+# The idea is to iterate through all the matrix and create a set of 'trues', 
+# which could be rightfully be avoided (but hasn't been for ease of understanding).
+# For each true-unvisited, we make it visited, and then look into 
+# it's neighbours and neighbours' neighbours or the belong_to's.
+# Only after this is over, we increment the result counter.
+####################################################################################
+
+
+def make_belong_set(item, trues):
+	# need to check if items at [i-1, j], [i, j-1], [i+1, j], [i, j+1] are in trues
+	i = item[0]
+	j = item[1]
+	belong_set = []
+	if (i-1, j) in trues.keys() and trues[(i-1, j)] == 'not_visited':
+		belong_set.append((i-1, j))
+	if (i, j-1) in trues.keys() and trues[(i, j-1)] == 'not_visited':
+		belong_set.append((i, j-1))
+	if (i+1, j) in trues.keys() and trues[(i+1, j)] == 'not_visited':
+		belong_set.append((i+1, j))
+	if (i, j+1) in trues.keys() and trues[(i, j+1)] == 'not_visited':
+		belong_set.append((i, j+1))
+	return belong_set
+
+def find_number_of_islands(row_no, col_no, matrix):
+	result_count = 0
+	# key: 'True' coordinates in matrix
+	# value: 'visited' or 'belongs_to' or 'not_visited'
+	trues = {}
+
+	# fill trues dict
+	for i in range(row_no):
+		for j in range(col_no):
+			if matrix[i][j]:
+				trues[(i, j)] = 'not_visited'
+
+	# go through trues, and for each not_visited, find its belongs_to set. 
+	# then for each of belongs_to iterate to find further on, until no belongs_to are left
+	# repeat
+	for item in trues.keys():
+		# item is an [i, j] list
+		if trues[item] == 'not_visited':
+			trues[item] = 'visited'
+			belong_set = make_belong_set(item, trues)
+			handle_belongs(belong_set, trues)
+			result_count += 1
+
+	print result_count
+
+def handle_belongs(belong_set, trues):
+	# for each item in belong_set
+	# 	make it visited, 
+	#	make its neighbours that are in trues as belongs_to
+	# repeat for as long as belong_set is not empty
+	for item in belong_set:
+		trues[item] = 'visited'
+		belong_set_ = make_belong_set(item, trues)
+		if not not belong_set:
+			handle_belongs(belong_set_, trues)
+
+# testing
+row = 4
+column = 4 
+matrix=[[True, True, False, True], 
+		[True, False, False, False], 
+		[False, False, True, False],
+		[True, False, False, True]]
+
+find_number_of_islands(row, column, matrix)