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63.py
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63.py
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from typing import List
class SolutionSimpleDP:
def uniquePathsWithObstacles(self, obstacleGrid: List[List[int]]) -> int:
m, n = len(obstacleGrid), len(obstacleGrid[0])
if obstacleGrid[-1][-1] == 1:
return 0
dp = [[0]*(n+1) for _ in range(m+1)]
dp[-2][-2] = 1
for j in range(m-1, -1, -1):
for i in range(n-1, -1, -1):
if obstacleGrid[j][i] == 1:
dp[j][i] = 0
elif i != n-1 or j != m-1:
dp[j][i] = dp[j+1][i] + dp[j][i+1]
return dp[0][0]
class SolutionReuseGrid:
def uniquePathsWithObstacles(self, grid: List[List[int]]) -> int:
m, n = len(grid), len(grid[0])
if grid[m-1][n-1] == 1:
return 0
# Now the cell value means that we can reach that cell with
# a given number of valid paths
grid[m-1][n-1] = 1
for j in range(m-2, -1, -1):
grid[j][n-1] = grid[j+1][n-1] if grid[j][n-1] == 0 else 0
for i in range(n-2, -1, -1):
grid[m-1][i] = grid[m-1][i+1] if grid[m-1][i] == 0 else 0
for j in range(m-2, -1, -1):
for i in range(n-2, -1, -1):
if grid[j][i] == 0:
grid[j][i] = grid[j+1][i] + grid[j][i+1]
else:
grid[j][i] = 0
return grid[0][0]
if __name__ == "__main__":
solvers = [SolutionSimpleDP(), SolutionReuseGrid()]
test_inputs = [
([[0,0,0],[0,1,0],[0,0,0]], 2),
([[0,1],[0,0]], 1),
([[0,0],[0,1]], 0),
([[0,0,0],[0,0,1],[0,1,0]], 0)
]
for solver in solvers:
for input, expected in test_inputs:
assert solver.uniquePathsWithObstacles(input) == expected