Vector2D(vector<vector<int>>& vec2d) : vec(vec2d) {

x = vec.begin();

if (x != vec.end()) {

y = x->begin();

adjustNextIter();

}

}

int next() {

const auto ret = *y;

++y;

adjustNextIter();

return ret;

}

bool hasNext() {

return x != vec.end() && y != x->end();

}

void adjustNextIter() {

while (x != vec.end() && y == x->end()) {

++x;

if (x != vec.end()) {

y = x->begin();

}

}

}

vector<vector<int>>& vec;

vector<vector<int>>::iterator x;

vector<int>::iterator y;