Asteroid_Collision.cpp

class Solution {
public:
    vector<int> asteroidCollision(vector<int>& asteroids) {

       vector<int> stack;

      for(const int a : asteroids)
      if( a > 0) {
        stack.push_back(a);
      }

      else {

        while (!stack.empty() && stack.back() > 0 && stack.back() < -a)
        stack.pop_back();

        if (stack.empty() || stack.back() < 0)
        stack.push_back(a);

        else if (stack.back() == -a)
        stack.pop_back();

      }

      return stack;
 
    }
};