# Asteroid Collision Solution – Leetcode coding challenge

A

The following asteroid collision problem is from Leetcode.

### The problem

We are given an array `asteroids` of integers representing asteroids in a row.

For each asteroid, the absolute value represents its size, and the sign represents its direction (positive meaning right, negative meaning left). Each asteroid moves at the same speed.

Find out the state of the asteroids after all collisions. If two asteroids meet, the smaller one will explode. If both are the same size, both will explode. Two asteroids moving in the same direction will never meet.

Example 1:

Example 2:

Example 3:

Example 4:

#### Constraints:

• `1 <= asteroids <= 104`
• `-1000 <= asteroids[i] <= 1000`
• `asteroids[i] != 0`

## Solution

We process from left to the right each integer value:

• We create a list to store the result `res`
• If a new asteroid value is positive, we add to the list as it will never collide with ones in `res`
• Else, we remove all the positive asteroids that smaller than the new value (negative)
• Then add the new value to `res` if `res` is empty or the last element is also negative (as it already processed in the previous run)
• If we have two opposite asteroids of the same size, then remove the last one.

Python code for asteroid collision problem:

Java code for asteroid collision problem: