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Commit 8ddc8de

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Solved Hackerrank FlatlandSpaceStations
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package hackerrank.FlatlandSpaceStations;
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import org.junit.jupiter.api.Assertions;
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import org.junit.jupiter.api.Disabled;
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import org.junit.jupiter.api.Test;
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import java.util.Arrays;
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/**
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* Flatland Space Stations
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* Flatland is a country with a number of cities,
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* some of which have space stations. Cities are
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* numbered consecutively and each has a road of
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* length 1km connecting it to the next city.
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*
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* It is not a circular route, so the first city
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* doesn't connect with the last city.
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*
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* Determine the maximum distance from any city
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* to its nearest space station.
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*
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* Function Description
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* Complete the flatlandSpaceStations function in the editor below.
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*
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* flatlandSpaceStations has the following parameter(s):
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*
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* int n: the number of cities
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* int c[m]: the indices of cities with a space station
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*
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* Returns
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* - int: the maximum distance any city is from a space station
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*
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* Input Format
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* The first line consists of two space-separated integers n and m.
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*
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* The second line contains space-separated integers,
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* the indices of each city that has a space-station.
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* These values are unordered and distinct.
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*
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* Constraints
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* 1 <= n <= 10^5
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* 1 <= m <= n
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*
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* There will be at least 1 city with a space station.
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* No city has more than one space station.
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*
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* Problem: https://www.hackerrank.com/challenges/flatland-space-stations/problem
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*
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* # Solution
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* The maximum distance any city is from a space station.
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*
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* Example 1
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* 5 2 n = 5, c[] size m = 2
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* 0 4 space stations
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*
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* There are five cities, c0,c1,c2,c3,c4.
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* c0 and c4 has space stations.
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* c2 has the maximum distance either to c0 or c4.
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* So maximum distance is 2.
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*
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* We only need to find the distances from those
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* cities which do not have the space station.
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*
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* Example 2
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* 6 6 n=6, m=6
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* 0 1 2 4 3 5
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* As all the cities have stations, maximum
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* distance from any city to a space station
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* is 0.
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*
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*
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*
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* Pseudocode
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* maxDistance = 0
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* We have to calculate the distance for each
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* city to another, so we need two loops.
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*
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* for i=0;i<cities.length;i++
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* for j=i+1;j<
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*
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* I think we just need to find maximum distance
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* between two stations, i.e. from a city to a
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* station between the stations.
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*
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* The distance from one (minimum) end point to
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* a space station.
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*
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* If there is only space station, calculate the
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* max distance from both ends.
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*
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* If there is only space station which is at
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* the either ends, get the distance from the
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* number of cities-1.
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*/
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public class FlatlandSpaceStations {
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public static int flatlandSpaceStations(
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int noOfCities,
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int[] spaceStations) {
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int noOfSpaceStations = spaceStations.length;
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if (noOfCities == noOfSpaceStations)
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return 0;
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else if (noOfCities == 2 && noOfSpaceStations == 1)
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return 1;
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else if (noOfCities == 3 && noOfSpaceStations == 2)
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return 1;
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else if (noOfSpaceStations == 1) {
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// if the space station is at first or last
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if (spaceStations[0] == 0 ||
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spaceStations[0] == noOfCities - 1)
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return noOfCities - 1;
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else {
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return Math.max(spaceStations[0],
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noOfCities - 1 - spaceStations[0]);
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}
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}
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Arrays.sort(spaceStations);
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// First and last cities are the space station.
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if (spaceStations[0] == 0 &&
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spaceStations[1] == noOfCities - 1)
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return (spaceStations[1] - spaceStations[0]) / 2;
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if (areSpaceStationsConsecutiveLast(
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spaceStations,
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noOfSpaceStations,
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noOfCities))
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return spaceStations[0];
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int maxDistance = 0;
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// If first city is not a space station
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if (spaceStations[0] != 0) {
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maxDistance = spaceStations[0];
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} else if ( spaceStations[0] == 0 ) {
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maxDistance = (spaceStations[1]-spaceStations[0])/2;
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}
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for (int i = 1; i < noOfSpaceStations-1; i++) {
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int distance = (spaceStations[i+1] - spaceStations[i])/2;
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if ( distance > maxDistance )
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maxDistance = distance;
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}
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// If last space station is not the last city
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if ( spaceStations[noOfSpaceStations-1] != noOfCities -1 ) {
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int lastSpaceStationDistance = noOfCities - 1 -
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spaceStations[noOfSpaceStations-1] ;
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return maxDistance > lastSpaceStationDistance ?
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maxDistance : lastSpaceStationDistance;
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}
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return maxDistance;
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}
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/**
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* The space stations are consecutive last,
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* i.e. They are the last ones.
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* Given 5 cities with 2 space stations that
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* are in the end. i.e. Cities 3 and 4 are
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* the space stations.
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*
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* Get the last station
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* Check if the last city is the last station,
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* spaceStations[noOfSpaceStations-1] == noOfCities-1
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*
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* Get the first station spaceStations[0]
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*
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* How to confirm that space stations are
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* consecutive last?
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*
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*/
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public static boolean areSpaceStationsConsecutiveLast(
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int[] spaceStations,
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int numberOfSpaceStations,
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int numberOfCities) {
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int lastSpaceStation = spaceStations[numberOfSpaceStations - 1];
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if ( lastSpaceStation != numberOfCities-1 )
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return false;
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int firstSpaceStation = spaceStations[0];
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int isLast = (lastSpaceStation - firstSpaceStation) -
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(numberOfSpaceStations - 1);
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return ( isLast == 0 ) ? true : false;
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}
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}
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