一步一步写算法（之prim算法 中）
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C）编写最小生成树，涉及创建、挑选和添加过程
MINI_GENERATE_TREE* get_mini_tree_from_graph(GRAPH* pGraph)
{
MINI_GENERATE_TREE* pMiniTree;
DIR_LINE pDirLine;
if(NULL == pGraph || NULL == pGraph->head)
return NULL;
pMiniTree = (MINI_GENERATE_TREE*)malloc(sizeof(MINI_GENERATE_TREE));
assert(NULL != pMiniTree);
memset(pMiniTree, 0, sizeof(MINI_GENERATE_TREE));
pMiniTree->node_num = 1;
pMiniTree->pNode = (int*)malloc(sizeof(int) * pGraph->count);
memset(pMiniTree->pNode, 0, sizeof(int) * pGraph->count);
pMiniTree->pNode[0] = pGraph->head->start;
while(1){
memset(&pDirLine, 0, sizeof(DIR_LINE));
get_dir_line_from_graph(pGraph, pMiniTree, &pDirLine);
if(pDirLine.start == 0)
break;
pMiniTree->line_num ++;
insert_line_into_queue(&pMiniTree->pLine, pDirLine.start, pDirLine.end, pDirLine.weight);
insert_node_into_mini_tree(&pDirLine, pMiniTree);
}
return pMiniTree;
}
MINI_GENERATE_TREE* get_mini_tree_from_graph(GRAPH* pGraph)
{
MINI_GENERATE_TREE* pMiniTree;
DIR_LINE pDirLine;
if(NULL == pGraph || NULL == pGraph->head)
return NULL;
pMiniTree = (MINI_GENERATE_TREE*)malloc(sizeof(MINI_GENERATE_TREE));
assert(NULL != pMiniTree);
memset(pMiniTree, 0, sizeof(MINI_GENERATE_TREE));
pMiniTree->node_num = 1;
pMiniTree->pNode = (int*)malloc(sizeof(int) * pGraph->count);
memset(pMiniTree->pNode, 0, sizeof(int) * pGraph->count);
pMiniTree->pNode[0] = pGraph->head->start;
while(1){
memset(&pDirLine, 0, sizeof(DIR_LINE));
get_dir_line_from_graph(pGraph, pMiniTree, &pDirLine);
if(pDirLine.start == 0)
break;
pMiniTree->line_num ++;
insert_line_into_queue(&pMiniTree->pLine, pDirLine.start, pDirLine.end, pDirLine.weight);
insert_node_into_mini_tree(&pDirLine, pMiniTree);
}
return pMiniTree;
}
d） 构建挑选函数，选择最合适的边
void get_dir_line_from_graph(GRAPH* pGraph, MINI_GENERATE_TREE* pMiniTree, DIR_LINE* pDirLine)
{
DIR_LINE* pHead;
DIR_LINE* prev;
VECTEX* pVectex;
LINE* pLine;
int index;
int start;
pHead = NULL;
for(index = 0; index < pMiniTree->node_num; index++){
start = pMiniTree->pNode[index];
pVectex = find_vectex_in_graph(pGraph->head, start);
pLine = pVectex->neighbor;
while(pLine){
insert_line_into_queue(&pHead, start, pLine->end, pLine->weight);
pLine = pLine->next;
}
}
if(NULL == pHead)
return;
delete_unvalid_line_from_list(&pHead, pMiniTree);
if(NULL == pHead)
return;
sort_for_line_list(&pHead);
memmove(pDirLine, pHead, sizeof(DIR_LINE));
while(pHead){
prev = pHead;
pHead = pHead->next;
free(prev);
}
return;
}
void get_dir_line_from_graph(GRAPH* pGraph, MINI_GENERATE_TREE* pMiniTree, DIR_LINE* pDirLine)
{
DIR_LINE* pHead;
DIR_LINE* prev;
VECTEX* pVectex;
LINE* pLine;
int index;
int start;
pHead = NULL;
for(index = 0; index < pMiniTree->node_num; index++){
start = pMiniTree->pNode[index];
pVectex = find_vectex_in_graph(pGraph->head, start);
pLine = pVectex->neighbor;
while(pLine){
insert_line_into_queue(&pHead, start, pLine->end, pLine->weight);
pLine = pLine->next;
}
}
if(NULL == pHead)
return;
delete_unvalid_line_from_list(&pHead, pMiniTree);
if(NULL == pHead)
return;
sort_for_line_list(&pHead);
memmove(pDirLine, pHead, sizeof(DIR_LINE));
while(pHead){
prev = pHead;
pHead = pHead->next;
free(prev);
}
return;
}
e）添加节点函数，将尚不是最小生成树的点纳入到最小生成树当中去
void insert_node_into_mini_tree(DIR_LINE* pLine, MINI_GENERATE_TREE* pMiniTree)
{
int index;
for(index = 0; index < pMiniTree->node_num; index ++){
if(pLine->start == pMiniTree->pNode[index]){
pMiniTree->pNode[pMiniTree->node_num++] = pLine->end;
return;
}
}
pMiniTree->pNode[pMiniTree->node_num++] = pLine->start;
return;
}
void insert_node_into_mini_tree(DIR_LINE* pLine, MINI_GENERATE_TREE* pMiniTree)
{
int index;
for(index = 0; index < pMiniTree->node_num; index ++){
if(pLine->start == pMiniTree->pNode[index]){
pMiniTree->pNode[pMiniTree->node_num++] = pLine->end;
return;
}
}
pMiniTree->pNode[pMiniTree->node_num++] = pLine->start;
return;
}
注意事项：
（1）d、e是c中调用的子函数，如果大家观察一下就明白了
（2）最小生成树是按照自顶向下的顺序编写的，虽然c中的子函数完成了，但是d中还有两个子函数没有着落
（3）d中的函数delete_unvalid_line_from_list、sort_for_line_list会在下一篇中继续介绍
（4）算法只要能够按照手工计算的流程编写出来，基本上问题不大，但是一些细节还是要小心注意的
【待续】