👋 Hello
This is solution for leetcode problem surrounded region from neetcode.io
Python BFS Solution
class Solution:
def solve(self, board: List[List[str]]) -> None:
ROWS, COLS = len(board), len(board[0])
def capture(r, c):
if r < 0 or c < 0 or r == ROWS or c == COLS or board[r][c] != "O":
return
board[r][c] = "T"
capture(r + 1, c)
capture(r - 1, c)
capture(r, c + 1)
capture(r, c - 1)
# 1. (DFS) Capture unsurrounded regions (O -> T)
for r in range(ROWS):
for c in range(COLS):
if board[r][c] == "O" and (r in [0, ROWS - 1] or c in [0, COLS - 1]):
capture(r, c)
# 2. Capture surrounded regions (O -> X)
for r in range(ROWS):
for c in range(COLS):
if board[r][c] == "O":
board[r][c] = "X"
# 3. Uncapture unsurrounded regions (T -> O)
for r in range(ROWS):
for c in range(COLS):
if board[r][c] == "T":
board[r][c] = "O"