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99 lines
3.3 KiB
Python
99 lines
3.3 KiB
Python
# An island in matrix is a group of linked areas, all having the same value.
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# This code counts number of islands in a given matrix, with including diagonal
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# connections.
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class Matrix: # Public class to implement a graph
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def __init__(self, graph: list[list[bool]]) -> None:
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"""
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Initialise matrix with number of rows, columns, and graph.
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>>> m = Matrix([[True, False, False, False],
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... [True, False, True, False],
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... [False, False, True, True]])
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>>> m.ROW
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3
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>>> m.COL
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4
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>>> m.graph
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[[True, False, False, False],
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[True, False, True, False],
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[False, False, True, True]]
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"""
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self.graph = graph
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self.ROW = len(graph)
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self.COL = len(graph[0])
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def is_safe(self, i: int, j: int, visited: list[list[bool]]) -> bool:
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"""
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Checks if the cell (i, j) can be visited.
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>>> visited = [[False, False, False],
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... [False, False, False],
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... [False, False, False]]
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>>> m = Matrix([[True, False, False],
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... [False, False, True],
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... [False, False, True]])
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>>> m.is_safe(0, 0, visited)
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True
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>>> m.is_safe(0, 2, visited)
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False
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>>> m.is_safe(-1, 2, visited)
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False
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>>> m.is_safe(1, 5, visited)
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False
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"""
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return (
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0 <= i < self.ROW
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and 0 <= j < self.COL
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and not visited[i][j]
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and self.graph[i][j]
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)
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def diffs(self, i: int, j: int, visited: list[list[bool]]) -> None:
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"""
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Checking all 8 elements surrounding nth element.
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>>> visited = [[False, False, False],
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... [False, False, False],
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... [False, False, False]]
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>>> m = Matrix([[True, True, False],
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... [False, True, False],
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... [True, False, True]])
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>>> m.diffs(0, 0, visited)
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>>> visited
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[[True, True, False],
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[False, True, False],
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[True, False, True]]
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"""
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row_nbr = [-1, -1, -1, 0, 0, 1, 1, 1] # Coordinate order
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col_nbr = [-1, 0, 1, -1, 1, -1, 0, 1]
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visited[i][j] = True # Make those cells visited
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for k in range(8):
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if self.is_safe(i + row_nbr[k], j + col_nbr[k], visited):
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self.diffs(i + row_nbr[k], j + col_nbr[k], visited)
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def count_islands(self) -> int:
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"""
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Counts the number of islands in the matrix.
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>>> m = Matrix([[True, True, False, False],
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... [False, True, False, True],
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... [True, False, False, True]])
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>>> m.count_islands()
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2
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>>> m2 = Matrix([[True, True, False],
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... [True, False, False],
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... [False, False, True]])
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>>> m2.count_islands()
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2
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"""
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visited = [[False for j in range(self.COL)] for i in range(self.ROW)]
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count = 0
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for i in range(self.ROW):
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for j in range(self.COL):
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if visited[i][j] is False and self.graph[i][j] == 1:
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self.diffs(i, j, visited)
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count += 1
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return count
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