1162. As Far from Land as Possible
class Solution {
public:
int maxDistance(vector<vector<int>>& grid) {
queue<pair<int, int>> Q;
int H = grid.size();
int W = grid[0].size();
int ans = -1;
int y, x;
vector<vector<bool> > visited(H, vector<bool>(W, false));
for(int ii = 0; ii < H; ii++) {
for(int jj = 0; jj < W; jj++) {
if(grid[ii][jj]) {
Q.push({
ii, jj});
visited[ii][jj] = true;
}
}
}
if(Q.size() == H*W || Q.size() == 0) return ans;
while(!Q.empty()) {
int len = Q.size();
for(int ii = 0; ii < len; ii++) {
auto A = Q.front();
Q.pop();
y = A.first - 1, x = A.second;
if(y >= 0 && y < H && !visited[y][x]) {
visited[y][x] = true;
Q.push({
y, x});
}
y = A.first + 1, x = A.second;
if(y >= 0 && y < H && !visited[y][x]) {
visited[y][x] = true;
Q.push({
y, x});
}
y = A.first, x = A.second - 1;
if(x >= 0 && x < W && !visited[y][x]) {
visited[y][x] = true;
Q.push({
y, x});
}
y = A.first, x = A.second + 1;
if(x >= 0 && x < W && !visited[y][x]) {
visited[y][x] = true;
Q.push({
y, x});
}
}
ans++;
}
return ans;
}
};