Dijkstra's algorithm的简单实现【java】

   在比较简单的情况下，当单条路径的距离固定为一的时候(比如计算分子中各个原子的距离)可以用表格来处理。只需要adjacency matrix.

private static int[][] doDijkstra(int[][] adjList) {
        int n = adjList.length;
        int[][] distMatrix = new int[n][n];
        for (int i = 0; i < n; ++i) {               //对于列表中的每一行
            for (int j = 0; j < n; ++j)                     //距离先设为无限大
                distMatrix[i][j] = Integer.MAX_VALUE;
            Set<Integer> layer = new HashSet<Integer>();//对于表中的每一列，考虑每个原子
            layer.add(i);                             
            distMatrix[i][i] = 0;                        
            int distance = 1;
            while (!layer.isEmpty()) {                        //当待考虑对象不为空时
                Set<Integer> nextLayer = new HashSet<Integer>();
                for (Integer c : layer) {                                  //考虑当前层的每个对象的所有neighbor
                    for (int d : adjList[c]) {                                  // 将这些neighbor与中心原子的距离记录下来
                        if (distMatrix[i][d] == Integer.MAX_VALUE) {
                            distMatrix[i][d] = distance;                        
                            nextLayer.add(d);                                    //将neighbors加入待考虑集合
                        }
                    }
                }
                layer = nextLayer;
                distance += 1;
            }
        }

可以看看和比较复杂的Dijkstra's algorithm伪代码的区别

1  function Dijkstra(Graph, source):
 2      for each vertex v in Graph:           // Initializations
 3          dist[v] := infinity ;              // Unknown distance function from source to v
 4          previous[v] := undefined ;         // Previous node in optimal path from source
 5      end for ;
 6      dist[source] := 0 ;                    // Distance from source to source
 7      Q := the set of all nodes in Graph ;
        // All nodes in the graph are unoptimized - thus are in Q
 8      while Q is not empty:                 // The main loop
 9          u := vertex in Q with smallest dist[] ;
10          if dist[u] = infinity:
11              break ;                        // all remaining vertices are inaccessible from source
12          fi ;
13          remove u from Q ;
14          for each neighbor v of u:         // where v has not yet been removed from Q.
15              alt := dist[u] + dist_between(u, v) ;
16              if alt < dist[v]:             // Relax (u,v,a)
17                  dist[v] := alt ;
18                  previous[v] := u ;
19              fi  ;
20          end for ;
21      end while ;
22      return dist[] ;
23  end Dijkstra.