最小生成树

//=======================================================================
// Use Adjacency Matrix and Prim algorithm Spanning MiniSpanTree
// BY:CHLAWS
// TIME:08-8-6
// PS:转载请别删除此备注
//=======================================================================
#include <stdio.h>
#include <stdlib.h>

#define MAX_VERTEX_NUM 20 //最大顶点数
typedef int AdjMatrix[MAX_VERTEX_NUM][MAX_VERTEX_NUM];//邻接矩阵类型
typedef char VertexType;
typedef struct {
VertexType vexs[MAX_VERTEX_NUM]; //顶点表
AdjMatrix arcs; //邻接矩阵
int vexnum,arcnum; //图的顶点数和弧数
}MGraph;

struct DNode{
VertexType adjvex;
int lowcost;
}closedge[MAX_VERTEX_NUM];

int LocateVex(MGraph G,char u);
void MiniSpanTree_PRIM(MGraph G,VertexType u);
void CreateMGraph(MGraph &G);
int mininum(struct DNode closedge[],int vexnum);
void main()
{
char u;
MGraph G;

printf("Text/n");
CreateMGraph(G);

printf("input you will start find first vertex:");
fflush(stdin);
scanf("%c",&u);

MiniSpanTree_PRIM(G,u);
}

void MiniSpanTree_PRIM(MGraph G,VertexType u)
{
int i,j,k;
k = LocateVex(G,u);

for (j=0; j<G.vexnum; ++j)
{
if(j!=k)
{
closedge[j].adjvex = u;
closedge[j].lowcost = G.arcs[k][j];
}
}
closedge[k].lowcost = 0;

for (i=1; i<G.vexnum; ++i)
{
k = mininum(closedge,G.vexnum);
printf("(%c, %c)/n",closedge[k].adjvex,G.vexs[k]);
closedge[k].lowcost = 0;

for(j=0; j<G.vexnum; ++j)
{
//这两个if是关键
//先保证两点间有路径,并且没被选入树的情况
if((G.arcs[k][j]>0 && closedge[j].lowcost>0) && (G.arcs[k][j]<closedge[j].lowcost))
{
closedge[j].adjvex = G.vexs[k];
closedge[j].lowcost= G.arcs[k][j];
}//再判断当两点间无直接路径时的情况
else if(closedge[j].lowcost<0)
{
closedge[j].adjvex = G.vexs[k];
closedge[j].lowcost = G.arcs[k][j];
}
}
}

}

int mininum(struct DNode closedge[], int vexnum)
{
int min = 10000;
int pos = -1;
while(vexnum--)
{
if((closedge[vexnum].lowcost > 0) && (min > closedge[vexnum].lowcost))
{
min = closedge[vexnum].lowcost;
pos = vexnum;
}
}
if(-1 == pos) { printf("closedge.lowcost find error!"); exit(-1); }
return pos;
}

void CreateMGraph(MGraph &G)
{
int i,j,k,w;
char v1,v2;
printf("Input vexnum & arcnum:");
scanf("%d,%d",&G.vexnum,&G.arcnum);
printf("Input Vertices:");
scanf("%s",G.vexs);
for (i=0;i<G.vexnum;i++)
for (j=0;j<G.vexnum;j++)
G.arcs[i][j]=-1;
for (k=0;k<G.arcnum;k++)
{
printf("Input Arcs(v1->v2 &w):/n");
fflush(stdin);
scanf("%c,%c,%d",&v1,&v2,&w);
i=LocateVex(G,v1);
j=LocateVex(G,v2);
G.arcs[i][j]=w;
G.arcs[j][i]=w;
}
return;
}

int LocateVex(MGraph G,char u)
{
int i;
for (i=0;i<G.vexnum;i++)
{
if (u == G.vexs[i]) return i;
}
if (i == G.vexnum)
{
printf("Error u!/n");
exit(1);
}

return 0;
}

//测试结果:
/*
Text
Input vexnum & arcnum:6,10
Input Vertices:ABCDEF
Input Arcs(v1->v2 &w):
A,B,6
Input Arcs(v1->v2 &w):
A,C,1
Input Arcs(v1->v2 &w):
A,D,5
Input Arcs(v1->v2 &w):
B,C,5
Input Arcs(v1->v2 &w):
B,E,3
Input Arcs(v1->v2 &w):
C,E,6
Input Arcs(v1->v2 &w):
C,F,4
Input Arcs(v1->v2 &w):
C,D,5
Input Arcs(v1->v2 &w):
D,F,2
Input Arcs(v1->v2 &w):
E,F,6
input you will start find first vertex:A
(A, C)
(C, F)
(F, D)
(C, B)
(B, E)
请按任意键继续. . .

*/