generic priority queue with functor comparator template argument

pq.cpp

#include <bits/stdc++.h>
using namespace std;

namespace my {
  template<class T, class F = less<T>>
    struct priority_queue {
      vector<T> v = {0};
      T i=0; // index if last elem
      F cmp = F();
      priority_queue() {}
      int size() {
	return i;
      }
      bool empty() {
	return size() == 0;
      }
      void bubbleup(int ind) {
	if (ind<=1) return;
	if (cmp(v[ind],v[ind>>1])) {
	  swap(v[ind],v[ind>>1]);
	  bubbleup(ind>>1);
	}
      }
      void push(int x) {
	++i;
	if (i>=(int)v.size()) {
	  v.push_back(x);
	} else {
	  v[i]=x;
	}
	bubbleup(i);
      }

      void bubbledown(int ind) {
	while (ind<<1 <= i) {
	  if ((ind<<1|1) <= i) {
	    if (cmp(v[ind<<1|1], v[ind<<1])) {
	      if (cmp(v[ind<<1|1], v[ind])) {
		swap(v[ind<<1|1], v[ind]);
		ind = ind<<1|1;
	      } else {
		break;
	      }
	    } else {
	      if (cmp(v[ind<<1], v[ind])) {
		swap(v[ind<<1], v[ind]);
		ind<<=1;
	      } else {
		break;
	      }
	    }
	  } else {
	    if (cmp(v[ind<<1], v[ind])) {
	      swap(v[ind<<1], v[ind]);
	      ind<<=1;
	    } else {
	      break;
	    }
	  }
	}
      }

      T pop() {
	if (size()==0) return 0;
	swap(v[1],v[i]);
	T ret = v[i--];
	bubbledown(1);
	return ret;
      }

      T top() {
	if (empty()) return -1; // bad way to handle error
	return v[1];
      }
    };
}



int main() {
  return 0;
}