Asteroid Collision

class Solution {
public:
    vector<int> asteroidCollision(vector<int>& a) {
        vector<int> st;
        for (int x : a) {
            bool alive = true;
            while (alive && x < 0 && !st.empty() && st.back() > 0) {
                if (st.back() < -x) st.pop_back();
                else if (st.back() == -x) { st.pop_back(); alive = false; }
                else alive = false;
            }
            if (alive) st.push_back(x);
        }
        return st;
    }
};

func asteroidCollision(a []int) []int {
    st := []int{}
    for _, x := range a {
        alive := true
        for alive && x < 0 && len(st) > 0 && st[len(st)-1] > 0 {
            top := st[len(st)-1]
            if top < -x {
                st = st[:len(st)-1]
            } else if top == -x {
                st = st[:len(st)-1]
                alive = false
            } else {
                alive = false
            }
        }
        if alive {
            st = append(st, x)
        }
    }
    return st
}

from typing import List

class Solution:
    def asteroidCollision(self, asteroids: List[int]) -> List[int]:
        st: List[int] = []
        for x in asteroids:
            alive = True
            while alive and x < 0 and st and st[-1] > 0:
                top = st[-1]
                if top < -x:
                    st.pop()
                elif top == -x:
                    st.pop()
                    alive = False
                else:
                    alive = False
            if alive:
                st.append(x)
        return st

var asteroidCollision = function(asteroids) {
    const st = [];
    for (const x of asteroids) {
        let alive = true;
        while (alive && x < 0 && st.length > 0 && st[st.length - 1] > 0) {
            const top = st[st.length - 1];
            if (top < -x) st.pop();
            else if (top === -x) { st.pop(); alive = false; }
            else alive = false;
        }
        if (alive) st.push(x);
    }
    return st;
};

class Solution {
    public int[] asteroidCollision(int[] asteroids) {
        Deque<Integer> st = new ArrayDeque<>();
        for (int x : asteroids) {
            boolean alive = true;
            while (alive && x < 0 && !st.isEmpty() && st.peek() > 0) {
                int top = st.peek();
                if (top < -x) st.pop();
                else if (top == -x) { st.pop(); alive = false; }
                else alive = false;
            }
            if (alive) st.push(x);
        }
        int[] out = new int[st.size()];
        for (int i = out.length - 1; i >= 0; i--) out[i] = st.pop();
        return out;
    }
}

function asteroidCollision(asteroids: number[]): number[] {
    const st: number[] = [];
    for (const x of asteroids) {
        let alive = true;
        while (alive && x < 0 && st.length > 0 && st[st.length - 1] > 0) {
            const top = st[st.length - 1];
            if (top < -x) st.pop();
            else if (top === -x) { st.pop(); alive = false; }
            else alive = false;
        }
        if (alive) st.push(x);
    }
    return st;
}