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Commit 60f44d7

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Hackerrank Challenges - Flatland Space Station - WIP
Algorithm build for three cities with space stations
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package hackerrank;
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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(int n, int[] c){
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int spaceStations = c.length;
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if ( n == 1 && spaceStations == 1 ) return 0;
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else if ( n == 2 && spaceStations == 1 ) return 1;
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else if ( n == 2 && spaceStations == 2 ) return 0;
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else if ( n == 3 && spaceStations == 2 ) return 1;
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if ( spaceStations == 1 ) {
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int firstSpaceStation = c[0];
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if ( n == 3 )
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return Math.max(firstSpaceStation, n-firstSpaceStation-1);
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else if ( firstSpaceStation == c.length-1 || c.length == 3 )
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return Math.max(firstSpaceStation-1, n-firstSpaceStation-1);
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else
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return Math.max(Math.abs(firstSpaceStation-1), n-firstSpaceStation);
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}
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Arrays.sort(c);
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int maxDistance = 0;
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int[] withLastCity = new int[spaceStations+1];
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withLastCity[spaceStations] = n-1;
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System.arraycopy(c, 0, withLastCity, 0, spaceStations);
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// maximum distance between space stations
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for(int i=0; i<spaceStations-1; i++){
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int distanceDiff = Math.abs(withLastCity[i]-withLastCity[i+1]);
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if ( maxDistance < distanceDiff)
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maxDistance = distanceDiff;
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}
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return maxDistance;
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}
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}
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class FlatlandSpaceStationsTest {
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@Test
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@Disabled
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void hasFourCitiesThreeStationsAtFirstSecondLast() {
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int n=4, expected=1; // Distance from city four to city 2
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int[] c={0,1,3};
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Assertions.assertEquals(expected,
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FlatlandSpaceStations.flatlandSpaceStations(n, c));
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/**
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* The current implementation fails.
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* Expected :1
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* Actual :2
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*
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* The maximum distance being calculated
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*/
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}
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@Test
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@Disabled
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void hasFourCitiesTwoStationsAtFirstAndSecond() {
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int n=4, expected=2; // Distance from city four to city 2
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int[] c={0,1};
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Assertions.assertEquals(expected,
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FlatlandSpaceStations.flatlandSpaceStations(n, c));
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/**
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* Get the maximum distance in space stations.
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* Here, 0 and 1 has 0 distance but there
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* 0 is the starting so no other cities and
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* there are cities after one as total cities
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* is 4.
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*/
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}
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@Test
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void hasThreeCityTwoStationsAtFirstAndThird() {
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int n=3, expected=1;
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int[] c={0,2};
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Assertions.assertEquals(expected,
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FlatlandSpaceStations.flatlandSpaceStations(n, c));
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}
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@Test
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void hasThreeCityTwoStations() {
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int n=3, expected=1;
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int[] c={0,1};
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Assertions.assertEquals(expected,
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FlatlandSpaceStations.flatlandSpaceStations(n, c));
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}
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@Test
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void hasTwoCityTwoStations() {
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int n=2, expected=0;
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int[] c={0,1};
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Assertions.assertEquals(expected,
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FlatlandSpaceStations.flatlandSpaceStations(n, c));
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}
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@Test
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void hasFourCitiesAndOneStationAtFirst() {
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int n=4;
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// Distance from first to fourth city 4-1 =3
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int expectedMaxDistance=3;
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int[] c={0};
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Assertions.assertEquals(expectedMaxDistance,
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FlatlandSpaceStations.flatlandSpaceStations(n, c));
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}
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@Test
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void hasFourCitiesAndOneStationAtThird() {
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int n=4, expectedMaxDistance=2;
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int[] c={2};
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Assertions.assertEquals(expectedMaxDistance,
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FlatlandSpaceStations.flatlandSpaceStations(n, c));
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}
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@Test
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void hasThreeCitiesAndOneStationAtThird() {
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int n=3, expectedMaxDistance=2;
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int[] c={2};
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Assertions.assertEquals(expectedMaxDistance,
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FlatlandSpaceStations.flatlandSpaceStations(n, c));
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}
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@Test
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void hasThreeCitiesAndOneStationAtSecond() {
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int n=3, expectedMaxDistance=1;
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int[] c={1};
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Assertions.assertEquals(expectedMaxDistance,
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FlatlandSpaceStations.flatlandSpaceStations(n, c));
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}
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@Test
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void hasThreeCitiesAndOneStationAtFirst() {
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/**
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* Case1: c0 has a station
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*
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* Get max distance from either end.
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*/
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int n=3, expectedMaxDistance=2;
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int[] c={0};
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Assertions.assertEquals(expectedMaxDistance,
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FlatlandSpaceStations.flatlandSpaceStations(n, c));
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}
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@Test
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void hasTwoCity() {
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int n=2, expected=1;
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int[] c={0};
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Assertions.assertEquals(expected,
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FlatlandSpaceStations.flatlandSpaceStations(n, c));
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}
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@Test
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void hasOneCity() {
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int n=1, expected=0;
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int[] c={0};
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Assertions.assertEquals(expected,
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FlatlandSpaceStations.flatlandSpaceStations(n, c));
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}
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}

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