# Space Battle - Amazon Top Interview Questions

### Problem Statement :

```There are a bunch of rockets in space lined up in a row.

You are given a list of integers nums representing each rocket's size and direction. If the number is positive it's going right, and if it's negative it's going left. The value of the number represents the rocket's size.

If two rockets collide, the smaller one will disappear and the larger one will continue on its course unchanged. If they are the same size and they collide, they'll both explode (both numbers are removed). If two rockets are moving in the same direction, they will never collide. The rockets start out equally spaced in the given order and all move at the same speed and become harmless after exploding.

Return the state of the rockets after all collisions.

Constraints

n ≤ 100,000 where n is the length of nums

Example 1

Input

nums = [1, 5, 3, -6]

Output

[-6]

Explanation

The last rocket will collide with everything to its left.

Example 2

Input

nums = [1, 5, 3, -6, 7]

Output

[-6, 7]

Explanation

-6 and 7 are going in separate directions, and the -6 rocket will destroy everything to its left.```

### Solution :

```                        ```Solution in C++ :

vector<int> solve(vector<int>& nums) {
vector<int> v;
stack<int> st;
int i = 0;
while (i < nums.size()) {
if (st.empty()) {
st.push(nums[i]);
i++;
continue;
}
int x = st.top();
if (x > 0 and nums[i] < 0) {
if (abs(x) < abs(nums[i]))
st.pop();
else if (abs(x) == abs(nums[i])) {
st.pop();
i++;
} else {
i++;
}
} else {
st.push(nums[i]);
i++;
}
}
while (!st.empty()) {
v.push_back(st.top());
st.pop();
}
reverse(v.begin(), v.end());
return v;
}```
```

```                        ```Solution in Python :

class Solution:
def solve(self, nums):
stack = []
right_to_left = []

for num in nums:
if num > 0:
stack.append(num)
else:
still_going = True
while stack and stack[-1] <= -num:
current = stack.pop()
if current == -num:
still_going = False
break

if not stack and still_going:
right_to_left.append(num)

return right_to_left + stack```
```

## Sparse Arrays

There is a collection of input strings and a collection of query strings. For each query string, determine how many times it occurs in the list of input strings. Return an array of the results. Example: strings=['ab', 'ab', 'abc'] queries=['ab', 'abc', 'bc'] There are instances of 'ab', 1 of 'abc' and 0 of 'bc'. For each query, add an element to the return array, results=[2,1,0]. Fun

## Array Manipulation

Starting with a 1-indexed array of zeros and a list of operations, for each operation add a value to each of the array element between two given indices, inclusive. Once all operations have been performed, return the maximum value in the array. Example: n=10 queries=[[1,5,3], [4,8,7], [6,9,1]] Queries are interpreted as follows: a b k 1 5 3 4 8 7 6 9 1 Add the valu

## Print the Elements of a Linked List

This is an to practice traversing a linked list. Given a pointer to the head node of a linked list, print each node's data element, one per line. If the head pointer is null (indicating the list is empty), there is nothing to print. Function Description: Complete the printLinkedList function in the editor below. printLinkedList has the following parameter(s): 1.SinglyLinkedListNode

## Insert a Node at the Tail of a Linked List

You are given the pointer to the head node of a linked list and an integer to add to the list. Create a new node with the given integer. Insert this node at the tail of the linked list and return the head node of the linked list formed after inserting this new node. The given head pointer may be null, meaning that the initial list is empty. Input Format: You have to complete the SinglyLink