Surrounded Regions
Problem Statement :
Given an m x n matrix board containing 'X' and 'O', capture all regions that are 4-directionally surrounded by 'X'. A region is captured by flipping all 'O's into 'X's in that surrounded region. Example 1: Input: board = [["X","X","X","X"],["X","O","O","X"],["X","X","O","X"],["X","O","X","X"]] Output: [["X","X","X","X"],["X","X","X","X"],["X","X","X","X"],["X","O","X","X"]] Explanation: Notice that an 'O' should not be flipped if: - It is on the border, or - It is adjacent to an 'O' that should not be flipped. The bottom 'O' is on the border, so it is not flipped. The other three 'O' form a surrounded region, so they are flipped. Example 2: Input: board = [["X"]] Output: [["X"]] Constraints: m == board.length n == board[i].length 1 <= m, n <= 200 board[i][j] is 'X' or 'O'.
Solution :
Solution in C :
void dfs(char** board, int rSize, int cSize, int r, int c) {
if (r < 0 || c < 0|| r > rSize - 1 || c > cSize - 1 || board[r][c] == 'X' || board[r][c] == 'T') return;
board[r][c] = 'T';
dfs(board, rSize, cSize, r + 1, c);
dfs(board, rSize, cSize, r - 1, c);
dfs(board, rSize, cSize, r, c + 1);
dfs(board, rSize, cSize, r, c - 1);
}
void solve(char** board, int boardSize, int* boardColSize) {
int rSize = boardSize, cSize = boardColSize[0];
for (int i = 0; i < cSize; i++) {
if (board[0][i] == 'O') dfs(board, rSize, cSize, 0, i);
if (board[rSize - 1][i] == 'O') dfs(board, rSize, cSize, rSize - 1, i);
}
for (int i = 0; i < rSize; i++) {
if (board[i][0] == 'O') dfs(board, rSize, cSize, i, 0);
if (board[i][cSize - 1] == 'O') dfs(board, rSize, cSize, i, cSize - 1);
}
for (int i = 0; i < rSize; i++) {
for (int j = 0; j < cSize; j++) {
if (board[i][j] == 'O') board[i][j] = 'X';
if (board[i][j] == 'T') board[i][j] = 'O';
}
}
}
Solution in C++ :
class Solution {
private:
int m, n;
vector<int> x = {+1, -1, 0, 0};
vector<int> y = {0, 0, +1, -1};
void dfs(int i, int j, vector<vector<char>>& board){
if(i>=0 && i<m && j>=0 && j<n && board[i][j]=='O'){
board[i][j] = '#';
for(int k=0; k<4; k++){
int newX = i+x[k];
int newY = j+y[k];
dfs(newX, newY, board);
}
}
}
public:
void solve(vector<vector<char>>& board) {
m=board.size(), n=board[0].size();
for(int i=0; i<m; i++){
if(board[i][0] == 'O') dfs(i, 0, board);
if(board[i][n-1] == 'O') dfs(i, n-1, board);
}
for(int j=0; j<n; j++){
if(board[0][j] == 'O') dfs(0, j, board);
if(board[m-1][j] == 'O') dfs(m-1, j, board);
}
for(int i=0; i<m; i++){
for(int j=0; j<n; j++){
if(board[i][j] == '#') board[i][j] = 'O';
else if(board[i][j] == 'O') board[i][j] = 'X';
}
}
}
};
Solution in Java :
class Solution {
public void solve(char[][] grid) {
for(int i=0;i<grid.length;i++){
if(grid[i][0]!='X')dfs(grid,i,0);
if(grid[i][grid[0].length-1]!='X')dfs(grid,i,grid[0].length-1);
}
for(int i=0;i<grid[0].length-1;i++){
if(grid[0][i]!='X')dfs(grid,0,i);
if(grid[grid.length-1][i]!='X')dfs(grid,grid.length-1,i);
}
swap(grid,'O','X');
swap(grid,'p','O');
}
void swap(char [][]grid,char p, char q){
for(int i=0;i<grid.length;i++){
for(int j=0;j<grid[0].length;j++){
if(grid[i][j]==p)grid[i][j]=q;
}
}
}
void dfs(char[][]grid, int i,int j){
if(!(i>=0 && j>=0 && i<grid.length && j<grid[0].length && grid[i][j]=='O')) return ;
grid[i][j]='p';
dfs(grid,i+1,j);
dfs(grid,i-1,j);
dfs(grid,i,j+1);
dfs(grid,i,j-1);
}
}
Solution in Python :
class Solution:
def nearme(self, return_list: List[List[int]], rownum:int,colnum:int, which:int)-> bool:
return (return_list[rownum][colnum-1] == which or return_list[rownum][colnum+1] == which or return_list[rownum+1][colnum] == which or return_list[rownum-1][colnum] == which)
def aroundme(self, return_list, rownum:int,colnum:int, which)-> bool:
return (return_list[rownum][colnum-1] == which and return_list[rownum][colnum+1] == which and return_list[rownum+1][colnum] == which and return_list[rownum-1][colnum] == which)
def createTag(self, board: List[List[str]]) -> List[List[int]]:
m = len(board)
n = len(board[0])
rowlow = 0
rowhigh = m - 1
columlow = 0
columhigh = n - 1
return_set = set()
for j in range(columlow,columhigh + 1):
if board[rowlow][j] == "O":
board[rowlow][j] = "C"
return_set.add((rowlow,j))
if board[rowhigh][j] == "O":
board[rowhigh][j] = "C"
return_set.add((rowhigh,j))
for i in range(rowlow +1,rowhigh):
if board[i][columlow] == "O":
board[i][columlow] = "C"
return_set.add((i,columlow))
if board[i][columhigh] == "O":
board[i][columhigh] = "C"
return_set.add((i,columhigh))
'''columlow += 1
rowlow += 1
columhigh -= 1
rowhigh -= 1
while columlow<=columhigh and rowlow<=rowhigh:
for j in range(columlow,columhigh+1):
if board[rowlow][j] == "O":
if self.nearme(return_list, rowlow, j, 2):
return_list[rowlow][j] = 2
elif self.aroundme(board,rowlow,j,"X"):
return_list[rowlow][j] = 1
else: return_list[rowlow][j] = 0
if board[rowhigh][j] == "O":
if self.nearme(return_list, rowhigh, j, 2):
return_list[rowhigh][j] = 2
elif self.aroundme(board,rowhigh,j,"X"):
return_list[rowhigh][j] = 1
else: return_list[rowhigh][j] = 0
for i in range(rowlow+1,rowhigh):
if board[i][columlow] == "O":
if self.nearme(return_list, i, columlow, 2):
return_list[i][columlow] = 2
elif self.aroundme(board,i,columlow,"X"):
return_list[i][columlow] = 1
else: return_list[i][columlow] = 0
if board[i][columhigh] == "O":
if self.nearme(return_list, i, columhigh, 2):
return_list[i][columhigh] = 2
elif self.aroundme(board,i,columhigh,"X"):
return_list[i][columhigh] = 1
else: return_list[i][columhigh] = 0
for j in reversed(range(columlow,columhigh+1)):
if board[rowlow][j] == "O":
if self.nearme(return_list, rowlow, j, 2):
return_list[rowlow][j] = 2
else: return_list[rowlow][j] = 0
if board[rowhigh][j] == "O":
if self.nearme(return_list, rowhigh, j, 2):
return_list[rowhigh][j] = 2
else: return_list[rowhigh][j] = 0
for i in reversed(range(rowlow+1,rowhigh)):
if board[i][columlow] == "O":
if self.nearme(return_list, i, columlow, 2):
return_list[i][columlow] = 2
else: return_list[i][columlow] = 0
if board[i][columhigh] == "O":
if self.nearme(return_list, i, columhigh, 2):
return_list[i][columhigh] = 2
else: return_list[i][columhigh] = 0
columlow += 1
rowlow += 1
columhigh -= 1
rowhigh -= 1
columlow -= 1
rowlow -= 1
columhigh += 1
rowhigh += 1
while columlow > 0 and n > columhigh and 0 < rowlow and m > rowhigh:
for j in range(columlow,columhigh+1):
if board[rowlow][j] == "O":
if self.nearme(return_list, rowlow, j, 2):
return_list[rowlow][j] = 2
else: return_list[rowlow][j] = 0
if board[rowhigh][j] == "O":
if self.nearme(return_list, rowhigh, j, 2):
return_list[rowhigh][j] = 2
else: return_list[rowhigh][j] = 0
for i in range(rowlow+1,rowhigh):
if board[i][columlow] == "O":
if self.nearme(return_list, i, columlow, 2):
return_list[i][columlow] = 2
else: return_list[i][columlow] = 0
if board[i][columhigh] == "O":
if self.nearme(return_list, i, columhigh, 2):
return_list[i][columhigh] = 2
else: return_list[i][columhigh] = 0
for j in reversed(range(columlow,columhigh+1)):
if board[rowlow][j] == "O":
if self.nearme(return_list, rowlow, j, 2):
return_list[rowlow][j] = 2
else: return_list[rowlow][j] = 0
if board[rowhigh][j] == "O":
if self.nearme(return_list, rowhigh, j, 2):
return_list[rowhigh][j] = 2
else: return_list[rowhigh][j] = 0
for i in reversed(range(rowlow+1,rowhigh)):
if board[i][columlow] == "O":
if self.nearme(return_list, i, columlow, 2):
return_list[i][columlow] = 2
else: return_list[i][columlow] = 0
if board[i][columhigh] == "O":
if self.nearme(return_list, i, columhigh, 2):
return_list[i][columhigh] = 2
else: return_list[i][columhigh] = 0
columlow -= 1
rowlow -= 1
columhigh += 1
rowhigh += 1'''
return return_set
def solve(self, board: List[List[str]]) -> None:
m = len(board)
n = len(board[0])
rowlow = 0
rowhigh = m - 1
columlow = 0
columhigh = n - 1
return_set = set()
for j in range(columlow,columhigh + 1):
if board[rowlow][j] == "O":
board[rowlow][j] = "C"
return_set.add((rowlow + 1,j))
if board[rowhigh][j] == "O":
board[rowhigh][j] = "C"
return_set.add((rowhigh - 1,j))
for i in range(rowlow +1,rowhigh):
if board[i][columlow] == "O":
board[i][columlow] = "C"
return_set.add((i,columlow + 1))
if board[i][columhigh] == "O":
board[i][columhigh] = "C"
return_set.add((i,columhigh - 1))
while return_set != set():
i,j = return_set.pop()
if rowlow < i < rowhigh and columlow < j < columhigh and board[i][j] == "O":
board[i][j] = "C"
return_set.add((i,j+1))
return_set.add((i,j-1))
return_set.add((i-1,j))
return_set.add((i+1,j))
for i in range(m):
for j in range(n):
if board[i][j] == "C": board[i][j] = "O"
elif board[i][j] == "O": board[i][j] = "X"
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