c语言写的prim算法,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】

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