How come I get local variable referenced before assignment error for cur_max while i can use copy_matrix within the dfs function?
class Solution:
def longestIncreasingPath(self, matrix: List[List[int]]) -> int:
rows, columns = len(matrix), len(matrix[0])
copy_matrix = {}
cur_max = 0
def dfs(r, c, prev):
if (r < 0 or c < 0 or
r == rows or c == columns or
matrix[r][c] <= prev):
return 0
if (r, c) in copy_matrix:
return copy_matrix[(r, c)]
max_length = 0
max_length = max(max_length, 1 + dfs(r + 1, c, matrix[r][c]))
max_length = max(max_length, 1 + dfs(r - 1, c, matrix[r][c]))
max_length = max(max_length, 1 + dfs(r, c + 1, matrix[r][c]))
max_length = max(max_length, 1 + dfs(r, c - 1, matrix[r][c]))
copy_matrix[(r, c)] = max_length
cur_max = max(cur_max, copy_matrix[(r, c)])
return max_length
for r in range(rows):
for c in range(columns):
dfs(r, c, -1)
return max(copy_matrix.values())
here's what i get
UnboundLocalError: local variable 'cur_max' referenced before assignment
cur_max = max(cur_max, copy_matrix[(r, c)])
Line 22 in dfs (Solution.py)
dfs(r, c, -1)
Line 28 in longestIncreasingPath (Solution.py)
ret = Solution().longestIncreasingPath(param_1)
Line 49 in _driver (Solution.py)
_driver()
Line 60 in <module> (Solution.py)
It is because for copy_matrix there is no local variable there, so it references the nonlocal variable present at line 6 ie copy_matrix = {}, while for cur_max it is being defined as a local variable in line 24 ie cur_max = max(cur_max, copy_matrix[(r, c)]), it is referencing nonlocal variables for copy_matirx, rows, columns but it is referencing the local variable for cur_max because it is being defined in the function and being referenced before assignment. What you probably want to do is this
def dfs(r, c, prev):
nonlocal cur_max
if (r < 0 or c < 0 or
r == rows or c == columns or
matrix[r][c] <= prev):
return 0
if (r, c) in copy_matrix:
return copy_matrix[(r, c)]
max_length = 0
max_length = max(max_length, 1 + dfs(r + 1, c, matrix[r][c]))
max_length = max(max_length, 1 + dfs(r - 1, c, matrix[r][c]))
max_length = max(max_length, 1 + dfs(r, c + 1, matrix[r][c]))
max_length = max(max_length, 1 + dfs(r, c - 1, matrix[r][c]))
copy_matrix[(r, c)] = max_length
cur_max = max(cur_max, copy_matrix[(r, c)])
return max_length