Question

我正在尝试编写一个函数int within(Graph g, Vertex s, int d, Vertex *vs)。该函数需要Graph g, Vertex s (source vertex), int d (an upper bound on distance), a pointer to array of vertices Vertex *vs (note, Vertex is typedef int)。该函数应该从源d中找到距离小于或等于s的所有顶点。它将所有这些顶点存储在vs[]数组中，该数组作为指针传递给函数。该函数返回vs[]中的元素数。

Examples of vertices that would be produced for various calls to the within() function:

问题

我已经实现了这个功能，如下所示。（）调用的唯一函数是findPath（），它也如下所示。但是，出于某种原因，这里有一个无限循环：

     for(v = i; v != s; v = path[v]){
        count++;     //HERE IS THE INFINITE LOOP
     }

我在这里要做的是计算从源顶点到当前顶点（v）的边数。

在（）函数中

// Find all vertices which are <= d edges from v
int within(Graph g, Vertex s, int d, Vertex *vs)
{
   int i;

   //distance from current vertex to source vertex 
   int distance = 0; 

   //index to count number of elements in vs[]
   int vsIndex = 0;

   //for each vertex in the graph
   for(i=0; i<g->nV; i++){

      //make sure current vertex is not the source vertex
      if(i != s){

         //find path from current vertex to source vertex
         findPath(g, s, i);

         //compute distance from current to source vertex
         Vertex v; 
         for(v = i; v != s; v = path[v]){
            count++;     //HERE IS THE INFINITE LOOP
         }

         */if distance from current to source is less than or equal to d,
         add current vertex to vs[] array and increment vsIndex.
         /*
         if(count <= d){
            vs[vsIndex++] = i;
         }
         //reset distance for next vertex to be checked
         count = 0;
      }
   }

   return vsIndex;
}

它是

的一部分的文件

#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
#include <string.h>
#include "Graph.h"
#include "Queue.h"
#include "Stack.h"

// graph representation (adjacency matrix)
typedef struct GraphRep {
   int   nV;    // #vertices
   int   nE;    // #edges
   int **edges; // matrix of booleans
} GraphRep;

// - these variables are used by various algorithms
static int *visited; // array [0//nV-1] of seen vertices
static int *path;    // array [0..V-1] of vertices in path

void findPath(Graph g, Vertex src, Vertex dest)
{
   int i;
   // array of "been visited" flags
   for (i = 0; i < g->nV; i++) visited[i] = 0;
   // array of path predecessor vertices
   Queue q = newQueue();
   QueueJoin(q, src); visited[src] = 1;
   int isFound = 0;
   while (!QueueIsEmpty(q) && !isFound) {
      Vertex y, x = QueueLeave(q);
      for (y = 0; y < g->nV; y++) {
         if (!g->edges[x][y]) continue;
         path[y] = x;
         if (y == dest) { isFound = 1; break; }
         if (!visited[y]) {
            QueueJoin(q, y);
            visited[y] = 1;
         }
      }
   }

}

图函数实现中的无限循环

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