LeetCode-in-Java

2271. Maximum White Tiles Covered by a Carpet

Medium

You are given a 2D integer array tiles where tiles[i] = [li, ri] represents that every tile j in the range li <= j <= ri is colored white.

You are also given an integer carpetLen, the length of a single carpet that can be placed anywhere.

Return the maximum number of white tiles that can be covered by the carpet.

Example 1:

Input: tiles = [[1,5],[10,11],[12,18],[20,25],[30,32]], carpetLen = 10

Output: 9

Explanation: Place the carpet starting on tile 10.

It covers 9 white tiles, so we return 9.

Note that there may be other places where the carpet covers 9 white tiles.

It can be shown that the carpet cannot cover more than 9 white tiles.

Example 2:

Input: tiles = [[10,11],[1,1]], carpetLen = 2

Output: 2

Explanation: Place the carpet starting on tile 10.

It covers 2 white tiles, so we return 2.

Constraints:

• 1 <= tiles.length <= 5 * 104
• tiles[i].length == 2
• 1 <= li <= ri <= 109
• 1 <= carpetLen <= 109
• The tiles are non-overlapping.

Solution

import java.util.Arrays;
import java.util.Comparator;

public class Solution {
    public int maximumWhiteTiles(int[][] tiles, int carpetLength) {
        Arrays.sort(tiles, Comparator.comparingInt(x -> x[0]));
        int currentCover = Math.min(tiles[0][1] - tiles[0][0] + 1, carpetLength);
        int maxCover = currentCover;
        int head = 1;
        int tail = 0;
        while (tail < tiles.length && head < tiles.length && maxCover < carpetLength) {
            if (tiles[head][1] - tiles[tail][0] + 1 <= carpetLength) {
                currentCover += tiles[head][1] - tiles[head][0] + 1;
                maxCover = Math.max(maxCover, currentCover);
                ++head;
            } else {
                int possiblePartialCoverOverCurrentHead =
                        carpetLength - (tiles[head][0] - tiles[tail][0]);
                maxCover = Math.max(maxCover, currentCover + possiblePartialCoverOverCurrentHead);
                currentCover = currentCover - (tiles[tail][1] - tiles[tail][0] + 1);
                ++tail;
            }
        }
        return maxCover;
    }
}

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