2013年 ACM 有为杯 Problem I （DAG）

有为杯  Problem I

DAG  有向无环图

A direct acylic graph(DAG)，is a directed graph with no directed cycles . That is ,it is formed by a collection of  vertion  of  vertices  and  directed  edges ,  each     edge

 connecting   one vertex to another,such that there is no way to way start at some vertex   v  and follow a squence of edges  that eventually  loops  back to v  again.

Given  a  DAG，output how many vertices each vetex can reach (including itself).

这是我根据题目写的算法，请各位品评、品评

#include<iostream>
#define g  10000
using namespace std;
int istr[g];//遍历过的点做标志
int a[g][g];

//深度遍历
void deeptaG(int k,int n){ 
int i;
istr[n]=1;
 for(i=0;i<k;i++){
  if(a[n][i]!=0 && !istr[i]){
  deeptaG(k,i);
  }
 }
}

int main(){

int o,p,i,k,j;
 int n,l;
 cin>>k>>l;
 while(l--){
 cin>>o>>p;
 a[o][p]=1;}

 for (i=0;i<k;i++){
  for (int h=0;h<k;h++)
  { istr[h]=0; }
 deeptaG(k,i);
 j=0;
 for(int u=0;u<k;u++)
 if(istr[u]==1){++j;}
cout<<j<<endl;
 }
return  0;
}