Maybe because you have large vector (arr) inside of function (solve). Try to make this vector global.

I think the problem is in your cond function, try this.

bool cond(const pair<int, int>& p1, const pair<int, int>& p2){
    return p1.first > p2.first || (p1.first == p2.first && p1.second < p2.second);
}