https://github.com/emahtab/distance-between-bus-stops
https://github.com/emahtab/distance-between-bus-stops
dijkstra-algorithm shortest-path
Last synced: 9 months ago
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- Host: GitHub
- URL: https://github.com/emahtab/distance-between-bus-stops
- Owner: eMahtab
- Created: 2021-09-24T13:20:26.000Z (about 4 years ago)
- Default Branch: main
- Last Pushed: 2021-09-24T13:31:44.000Z (about 4 years ago)
- Last Synced: 2025-02-02T03:25:53.372Z (11 months ago)
- Topics: dijkstra-algorithm, shortest-path
- Homepage:
- Size: 26.4 KB
- Stars: 1
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# Distance between bus stops
## https://leetcode.com/problems/distance-between-bus-stops
A bus has n stops numbered from 0 to n - 1 that form a circle. We know the distance between all pairs of neighboring stops where distance[i] is the distance between the stops number i and (i + 1) % n.
The bus goes along both directions i.e. clockwise and counterclockwise.
Return the shortest distance between the given start and destination stops.
## Dijkstra Implementation 1 : Memory Limit Exceeded
```java
class Solution {
public int distanceBetweenBusStops(int[] distance, int start, int destination) {
if(start == destination)
return 0;
int n = distance.length;
int[] shortestDistances = new int[n];
Arrays.fill(shortestDistances, Integer.MAX_VALUE);
shortestDistances[start] = 0;
PriorityQueue minHeap = new PriorityQueue<>((v1, v2) -> v1[1] - v2[1]);
minHeap.offer(new int[]{start, 0});
// create adjacency matrix
int[][] adjMatrix = new int[n][n];
boolean[] visited = new boolean[n];
for(int i = 0; i < n; i++) {
Arrays.fill(adjMatrix[i], -1);
}
for(int i = 0; i < distance.length; i++) {
adjMatrix[i][(i+1) % n] = distance[i];
adjMatrix[(i+1) % n][i] = distance[i];
}
while(!minHeap.isEmpty()) {
int[] busStop = minHeap.poll();
if(busStop[0] == destination)
return busStop[1];
if(visited[busStop[0]])
continue;
visited[busStop[0]] = true;
// check neighboring stops
for(int v = 0; v < n; v++) {
if(adjMatrix[busStop[0]][v] != -1) {
int dU = busStop[1];
int distanceToNeighbor = adjMatrix[busStop[0]][v];
if(dU + distanceToNeighbor < shortestDistances[v]) {
shortestDistances[v] = dU + distanceToNeighbor;
minHeap.offer(new int[]{v, shortestDistances[v]});
}
}
}
}
return -1;
}
}
```
## Dijkstra Implementation 2 : Without using Adjacency Matrix
```java
class Solution {
public int distanceBetweenBusStops(int[] distance, int start, int destination) {
if(start == destination)
return 0;
int n = distance.length;
int[] shortestDistances = new int[n];
Arrays.fill(shortestDistances, Integer.MAX_VALUE);
shortestDistances[start] = 0;
PriorityQueue minHeap = new PriorityQueue<>((v1, v2) -> v1[1] - v2[1]);
minHeap.offer(new int[]{start, 0});
boolean[] visited = new boolean[n];
while(!minHeap.isEmpty()) {
int[] busStop = minHeap.poll();
if(busStop[0] == destination)
return busStop[1];
if(visited[busStop[0]])
continue;
visited[busStop[0]] = true;
// check neighboring stops
int nextNeighbor = (busStop[0] + 1) % n;
int prevNeighbor = busStop[0] == 0 ? n-1 : busStop[0] - 1;
// check next neighbor
int d = distance[busStop[0]];
if(busStop[1] + d < shortestDistances[nextNeighbor]) {
shortestDistances[nextNeighbor] = busStop[1] + d;
minHeap.offer(new int[]{nextNeighbor , shortestDistances[nextNeighbor]});
}
// check previous neighbor
d = distance[prevNeighbor];
if(busStop[1] + d < shortestDistances[prevNeighbor]) {
shortestDistances[prevNeighbor] = busStop[1] + d;
minHeap.offer(new int[]{prevNeighbor , shortestDistances[prevNeighbor]});
}
}
return -1;
}
}
```