LeetCode-in-Java

2008. Maximum Earnings From Taxi

Medium

There are n points on a road you are driving your taxi on. The n points on the road are labeled from 1 to n in the direction you are going, and you want to drive from point 1 to point n to make money by picking up passengers. You cannot change the direction of the taxi.

The passengers are represented by a 0-indexed 2D integer array rides, where rides[i] = [starti, endi, tipi] denotes the ith passenger requesting a ride from point starti to point endi who is willing to give a tipi dollar tip.

For each passenger i you pick up, you earn endi - starti + tipi dollars. You may only drive at most one passenger at a time.

Given n and rides, return the maximum number of dollars you can earn by picking up the passengers optimally.

Note: You may drop off a passenger and pick up a different passenger at the same point.

Example 1:

Input: n = 5, rides = [[2,5,4],[1,5,1]]

Output: 7

Explanation: We can pick up passenger 0 to earn 5 - 2 + 4 = 7 dollars.

Example 2:

Input: n = 20, rides = [[1,6,1],[3,10,2],[10,12,3],[11,12,2],[12,15,2],[13,18,1]]

Output: 20

Explanation: We will pick up the following passengers:

• Drive passenger 1 from point 3 to point 10 for a profit of 10 - 3 + 2 = 9 dollars.

• Drive passenger 2 from point 10 to point 12 for a profit of 12 - 10 + 3 = 5 dollars.

• Drive passenger 5 from point 13 to point 18 for a profit of 18 - 13 + 1 = 6 dollars.

We earn 9 + 5 + 6 = 20 dollars in total.

Constraints:

• 1 <= n <= 105
• 1 <= rides.length <= 3 * 104
• rides[i].length == 3
• 1 <= starti < endi <= n
• 1 <= tipi <= 105

Solution

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Solution {
    public long maxTaxiEarnings(int n, int[][] rides) {
        if (rides.length == 1) {
            return calculateEarnings(rides[0]);
        }

        Map<Integer, List<int[]>> map = new HashMap<>();
        for (int[] ride : rides) {
            map.compute(ride[1], (k, v) -> (v == null) ? new ArrayList<>() : v).add(ride);
        }

        long[] maximisedEarnings = new long[n + 1];
        Arrays.fill(maximisedEarnings, 0);
        for (int i = 1; i < maximisedEarnings.length; i++) {
            maximisedEarnings[i] = maximisedEarnings[i - 1];
            List<int[]> passengers = map.get(i);
            if (passengers != null) {
                for (int[] passenger : passengers) {
                    final int earning = calculateEarnings(passenger);
                    maximisedEarnings[i] =
                            Math.max(
                                    maximisedEarnings[i],
                                    maximisedEarnings[passenger[0]] + earning);
                }
            }
        }
        return maximisedEarnings[n];
    }

    private int calculateEarnings(final int[] currentRide) {
        return currentRide[1] - currentRide[0] + currentRide[2];
    }
}

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