LeetCode 1274: Number of Ships in a Rectangle Solution

Master LeetCode problem 1274 (Number of Ships in a Rectangle), 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.

1274. Number of Ships in a Rectangle

Hard

Array Divide and Conquer Interactive

Problem Explanation

Explanation:

This problem can be solved using a divide and conquer approach along with binary search. The idea is to recursively divide the given rectangle into smaller sub-rectangles until the rectangle contains only one ship or no ships at all. At each step, we check if the current rectangle contains any ships. If a ship is found in a rectangle, we split the rectangle into four smaller rectangles and continue the search in each smaller rectangle until we reach a single point. This approach helps in reducing the search space efficiently.

Steps:

Define a recursive function that takes the top-left and bottom-right coordinates of the current rectangle, along with a list of ships within the rectangle.
Check if there are any ships within the current rectangle. If not, return 0.
If there are ships, check if the rectangle contains only one ship. If so, return 1.
Otherwise, split the rectangle into four smaller rectangles and recursively search for ships in each smaller rectangle.
Repeat the above steps until we reach a single point or no ships are found.

Time Complexity:

The time complexity of this approach is O(N log N), where N is the number of ships in the given rectangle. The divide and conquer approach helps in efficiently reducing the search space.

Space Complexity:

The space complexity of this approach is O(log N) for the recursive call stack.: :

Solution Code

class Solution {
    public int countShips(Sea sea, int[] topRight, int[] bottomLeft) {
        return countShipsHelper(sea, topRight, bottomLeft);
    }
    
    private int countShipsHelper(Sea sea, int[] topRight, int[] bottomLeft) {
        if (!sea.hasShips(topRight, bottomLeft)) {
            return 0;
        }
        
        if (topRight[0] == bottomLeft[0] && topRight[1] == bottomLeft[1]) {
            return 1;
        }
        
        int midX = (topRight[0] + bottomLeft[0]) / 2;
        int midY = (topRight[1] + bottomLeft[1]) / 2;
        
        return countShipsHelper(sea, new int[]{midX, midY}, bottomLeft) +
               countShipsHelper(sea, new int[]{topRight[0], midY}, new int[]{midX + 1, bottomLeft[1]}) +
               countShipsHelper(sea, topRight, new int[]{midX + 1, midY + 1}) +
               countShipsHelper(sea, new int[]{midX, topRight[1]}, new int[]{bottomLeft[0], midY + 1});
    }
}

Try It Yourself

Loading code editor...

Frequently Asked Questions

How to solve LeetCode 1274 (Number of Ships in a Rectangle)?

This page provides optimized solutions for LeetCode problem 1274 (Number of Ships in a Rectangle) in Java, C++, and Python, along with a detailed explanation and an interactive code editor to test your code.

What is the time complexity of LeetCode 1274 (Number of Ships in a Rectangle)?

The time complexity for LeetCode 1274 (Number of Ships in a Rectangle) varies by solution. Check the detailed explanation section for specific complexities in Java, C++, and Python implementations.

Can I run code for LeetCode 1274 on DevExCode?

Yes, DevExCode provides an interactive code editor where you can write, test, and run your code for LeetCode 1274 in Java, C++, or Python.

Back to LeetCode Solutions