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remove-islands.py
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remove-islands.py
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# REMOVE ISLANDS
# O(wh) time and space
def removeIslands(matrix):
# Write your code here.
m = len(matrix)
n = len(matrix[0])
for i in range(n):
if matrix[0][i] == 1:
markAllBorderBlacks(matrix, 0, i)
for i in range(m):
if matrix[i][0] == 1:
markAllBorderBlacks(matrix, i, 0)
for i in range(n):
if matrix[m-1][i] == 1:
markAllBorderBlacks(matrix, m-1, i)
for i in range(m):
if matrix[i][n-1] == 1:
markAllBorderBlacks(matrix, i, n-1)
removeAllIslands(matrix)
return matrix
def markAllBorderBlacks(matrix, i, j):
if not 0 <= i < len(matrix) or not 0 <= j < len(matrix[0]) or matrix[i][j] in [0, 'K']:
return
matrix[i][j] = 'K'
markAllBorderBlacks(matrix, i+1, j)
markAllBorderBlacks(matrix, i, j+1)
markAllBorderBlacks(matrix, i-1, j)
markAllBorderBlacks(matrix, i, j-1)
def removeAllIslands(matrix):
for i in range(len(matrix)):
for j in range(len(matrix[0])):
if matrix[i][j] == 1:
matrix[i][j] = 0
if matrix[i][j] == 'K':
matrix[i][j] = 1
# O(wh) time and space
def removeIslands(matrix):
# Write your code here.
for row in range(len(matrix)):
for col in range(len(matrix[0])):
isRowBorder = row == 0 or row == len(matrix) - 1
isColBorder = col == 0 or col == len(matrix[0]) - 1
isBorder = isRowBorder or isColBorder
if not isBorder:
continue
print(matrix)
if matrix[row][col] == 1:
changeConnectedBlacks(matrix, row, col)
for i in range(len(matrix)):
for j in range(len(matrix[0])):
if matrix[i][j] == 1:
matrix[i][j] = 0
if matrix[i][j] == -1:
matrix[i][j] = 1
return matrix
def changeConnectedBlacks(matrix, i, j):
stack = [[i, j]]
while len(stack) > 0:
temp = stack.pop()
i = temp[0]
j = temp[1]
if matrix[i][j] == 0 or matrix[i][j] == -1:
continue
matrix[i][j] = -1
unvisitedNeighbors = getAllNeighbors(matrix, i, j)
for neighbor in unvisitedNeighbors:
stack.append(neighbor)
def getAllNeighbors(matrix, i, j):
neighbors = []
if not i == 0:
neighbors.append([i-1, j])
if not i == len(matrix) - 1:
neighbors.append([i+1, j])
if not j == 0:
neighbors.append([i, j-1])
if not j == len(matrix[0]) - 1:
neighbors.append([i, j+1])
return neighbors