When I am solving questions on Dijkstra's, I had basically two-way (or Java template) to write code for Dijkstra's, but for some questions, problem solved by both ways (or Dijkstra's Java templates) (https://leetcode.com/problems/network-delay-time/) are accepted and for some (e.g., https://leetcode.com/problems/path-with-minimum-effort/), anyone is able to solve the question.
For a graph (represented in Adjacency List):
ArrayList<int[]>[] graph = new ArrayList[n]; // n represents number of nodes.
1. Dijkstra's - One way
boolean[] vis = new boolean[n];
int[] dist = new int[n];
Arrays.fill( dist, Integer.MAX_VALUE );
PriorityQueue<Integer> q = new PriorityQueue<>( (a,b) -> dist[a] - dist[b] );
q.add( 0 ); // Starting node
dist[start] = 0;
while( !q.isEmpty() )
{
int node = q.poll();
if( vis[node] )
continue;
vis[node] = true;
// traversing neighboours
for( int[] nb : graph[node] )
{
int node2 = nb[0];
int weight = nb[1];
if( !vis[node2] && dist[node2] > dist[node] + weight )
{
dist[node2] = dist[node] + weight;
q.add( node2 );
}
}
}
2. Dijkstra's - Second way
boolean[] vis = new boolean[n];
int[] dist = new int[n];
Arrays.fill( dist, Integer.MAX_VALUE );
PriorityQueue<int[]> q = new PriorityQueue<>( (a,b) -> a[1] - b[1] );
q.add( new int[2] ); // Starting node
dist[start] = 0;
while( !q.isEmpty() )
{
int node = q.peek()[0];
int dis = q.peek()[1];
if( vis[node] )
continue;
vis[node] = true;
// traversing neighboours
for( int[] nb : graph[node] )
{
int node2 = nb[0];
int weight = nb[1];
if( !vis[node2] && dist[node2] > dis + weight )
{
dist[node2] = dis + weight;
q.add( new int[] { node2, dist[node2] } );
}
}
}
Can anyone, help me to know which is the right way (1st or 2nd).
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