# Runtime Error for maximum recursion depth. How can I optimize my code?

• It indicates Line 31: RuntimeError: maximum recursion depth exceeded in cmp.
How can I optimize my code?

``````class Solution:
# @param {character[][]} board
# @return {void} Do not return anything, modify board in-place instead.
def solve(self, board):
m = len(board)
if m != 0:
n = len(board[0])

self.visit = []
for i in range(m):
self.visit.append([False] * n)

for i in range(n):
if not self.visit[0][i]:
self.dfs(board, 0, i, m, n)
if not self.visit[m-1][i]:
self.dfs(board, m-1, i, m, n)

for i in range(m):
if not self.visit[i][0]:
self.dfs(board, i, 0, m, n)
if not self.visit[i][n-1]:
self.dfs(board, i, n-1, m, n)

for i in range(m):
for j in range(n):
if not self.visit[i][j]:
board[i][j] = 'X'

def dfs(self, board, i, j, m, n):
if board[i][j] == 'X' or self.visit[i][j]:
return

self.visit[i][j] = True

if i > 0 and not self.visit[i-1][j]:
self.dfs(board, i-1, j, m, n)

if i < m-1 and not self.visit[i+1][j]:
self.dfs(board, i+1, j, m, n)

if j > 0 and not self.visit[i][j-1]:
self.dfs(board, i, j-1, m, n)

if j < n-1 and not self.visit[i][j+1]:
self.dfs(board, i, j+1, m, n)``````

• If you look at the test case, you'll see that it's a zig-zag-line with length > 30000. Python usually has a recursion limit of 1000. I believe the OJ here at least sometimes increases that limit. You can try increasing it yourself with `sys.setrecursionlimit`, but it's unsafe. You'll likely have to give up this recursive approach or switch to another language.

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