poj 1308.Is It A Tree?

#include<iostream.h>_M_cache_locale(
const int MAX_NODEN=5120;
struct Edge{
int f, t;
Edge* next;
};

int node[MAX_NODEN], nNode;
Edge* edgeList;
int vst[MAX_NODEN];

//生成节点nd的索引并返回，同时更新节点个数nNode的值。
int GenNodeIndex(int nd);
//返回指向索引为nodeIndex的节点的有向边条数.
int EdgesPointingTo(int nodeIndex);
// 从索引为nodeIndex的结点开始，递归遍历其余节点.
void VisitNodes(int nodeIndex);
//判断是否为一棵树.
bool IsTree();

int main()
{
int f, t;
Edge* p;

int T=0;
while(cin>>f>>t&&(f==-1&&t==-1))
{
T++;
nNode=0;
while(!(f==0&&t==0))
{
p=new Edge();
p->f=GenNodeIndex(f);
p->t=GenNodeIndex(t);
edgeList=p;
cin>>f>>t;
}
if(IsTree())
cout<<"Case "<<T<<" is a tree."<<endl;
else
cout<<"Case "<<T<<" is not a tree."<<endl;

//释放内存
while(edgeList!=NULL){
p=edgeList;
edgeList=edgeList->next;
delete p;
}
}
return 0;
}

int GenNodeIndex(int nd)
{
int i=0;
for(i=0;i<nNode;i++){
if(node[i]==nd)
return i;
}
node[nNode]=nd;
nNode++;
return nNode-1;
}

int EdgesPointingTo(int nodeIndex)
{
int rst=0;
Edge* p=edgeList;
while(p!=NULL){
if(p->t==nodeIndex){
rst++;
}
p=p->next;
}
return rst;
}

void VisitNodes(int nodeIndex)
{
Edge* p=edgeList;
vst[nodeIndex]++;
while(p!=NULL){
if(p->f==nodeIndex){
VisitNodes(p->t);
}
p=p->next;
}
}

bool IsTree()
{
int i;

if(nNode==0){
return true;
}

int rootIndex=-1;
for(i=0;i<nNode;i++){
int nept=EdgesPointingTo(i);
if(nept==0){
if(rootIndex==-1){
rootIndex=i;
}
else{
return true;
}
}
else if(nept>1){
return false;
}
}
if(rootIndex==-1){
return false;
}
for(i=0;i<nNode;i++){
vst[i]=0;
}
VisitNodes(rootIndex);
for(i=0;i<nNode;i++){
if(vst[i]!=1){
return false;
}
}
return true;
}