AsteroidCollision.cpp

class Solution {
public:
    vector<int> asteroidCollision(vector<int>& asteroids) {
        stack<int>st;
        vector<int>res;
        int i,sz=asteroids.size();
        for(i=0;i<sz;i++)
        {
            if(asteroids[i]>0)
            {
                st.push(asteroids[i]);
            }
            else
            {
                while((!st.empty()) && (st.top()>0) && (st.top()<abs(asteroids[i])))
                    st.pop();
                if((st.empty()) || (st.top()<0))
                    st.push(asteroids[i]);
                else if((st.top()>0) && (st.top() == abs(asteroids[i])))
                    st.pop();
            }
        }
        while(!st.empty())
        {
            res.push_back(st.top());
            st.pop();
        }
        reverse(res.begin(),res.end());
        return res;
    }
};