[英]How to determine if a vertex can be reached in a directed graph using breadth first search
當試圖確定有向圖中的頂點是否可達時,我使用廣度優先搜索來從我的源頂點到目標頂點遍歷圖形。 然而,當我比較我在bfs期間從隊列中彈出的內容(應該是我訪問過的每個頂點)時,它只返回false並且從不在任何實例中為真,盡管我知道圖形在某些情況下可以返回true,可以幫助一些我出去?
這是我的代碼
template <typename E>
bool Graph<E>::isReachable(E fromKey, E toKey) const
{
Edge* tmpEdge;
Edge* pred;
Edge* edgeWalk;
Vertex* walkPtr;
Vertex* toPtr;
Vertex* tmp;
Vertex* tmpFrom;
Vertex* tmpTo;
queue<Vertex*> q;
/* find source vertex */
tmpFrom = first;
while (tmpFrom != NULL && fromKey > tmpFrom->data)
tmpFrom = tmpFrom->pNextVertex;
if (tmpFrom == NULL || fromKey != tmpFrom->data)
return false;
/* locate destination vertex */
tmpTo = first;
while (tmpTo != NULL && toKey > tmpTo->data)
tmpTo = tmpTo->pNextVertex;
if (tmpTo == NULL || toKey != tmpTo->data)
return false;
walkPtr = first;
while (walkPtr != NULL)
{
walkPtr->processed = 0;
walkPtr = walkPtr->pNextVertex;
}
walkPtr = first;
while (walkPtr != NULL)
{
if (walkPtr->processed < 2)
{
if (walkPtr->processed < 1)
{
q.push(walkPtr);
walkPtr->processed = 1;
}
}
while (!q.empty())
{
tmp = q.front();
q.pop();
tmp->processed = 2;
edgeWalk = tmp->pEdge;
while (edgeWalk != NULL)
{
toPtr = edgeWalk->destination;
if (toPtr->processed == 0)
{
toPtr->processed = 1;
q.push(toPtr);
}
edgeWalk = edgeWalk->pNextEdge;
}
if (tmpTo->processed = 2)
return true;
}
return false;
}
}
您的頂點列表是否正確排序? 如果不是(很可能),您將無法找到from或to鍵並返回false。 而且我說“可能”,因為你的循環底部有幾個問題,其中一個( tmpTo->processed = 2
;你應該使用==
)將導致函數一直返回true。
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