LeetCode 2751: Robot Collisions Solution

Master LeetCode problem 2751 (Robot Collisions), a hard challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

2751. Robot Collisions

Hard

Array Stack Sorting Simulation

Problem Explanation

Explanation:

To solve this problem, we can simulate the movements of the robots and handle collisions as described. We can use a priority queue to keep track of the robots in the order of their positions.

Initialize a priority queue to store the robots based on their positions.
Iterate through the robots in the order of their indices.
For each robot:
- Calculate its next position based on its direction.
- Check for collisions with other robots in the priority queue.
- Resolve collisions based on health values.
- Update the health of surviving robots.
Return the health values of the surviving robots in the order they were given in the input.

Time complexity: O(n log n) where n is the number of robots. Space complexity: O(n) for the priority queue.

Solution Code

import java.util.*;

class Solution {
    public int[] robotCollisions(int[] positions, int[] healths, String directions) {
        int n = positions.length;
        PriorityQueue<int[]> pq = new PriorityQueue<>((a, b) -> Integer.compare(a[0], b[0]));

        for (int i = 0; i < n; i++) {
            pq.offer(new int[]{positions[i], healths[i], i});
        }

        while (!pq.isEmpty()) {
            int[] current = pq.poll();
            int nextPos = current[0] + (directions.charAt(current[2]) == 'R' ? 1 : -1);

            if (!pq.isEmpty() && nextPos == pq.peek()[0]) {
                int[] next = pq.poll();
                if (current[1] > next[1]) {
                    pq.offer(new int[]{nextPos, current[1] - next[1], current[2]});
                } else if (current[1] < next[1]) {
                    pq.offer(new int[]{next[0], next[1] - current[1], next[2]});
                }
            }
        }

        List<Integer> result = new ArrayList<>();
        for (int[] robot : pq) {
            result.add(robot[1]);
        }

        return result.stream().mapToInt(i -> i).toArray();
    }
}

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