poj 1094 Sorting It All Out_拓扑排序

题意：是否唯一确定顺序，根据情况输出

#include <iostream>
#include<cstdio>
#include<cstring>
#include<stack>
using namespace std;
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
#define N 30
int n,m;
int map[N][N],indegree[N],list[N];
int toposort(int n){
	int in[N],flag,t,num;
	memcpy(in,indegree,sizeof(indegree));//复制入度数组，以免对主函数中的indegree有影响
	stack<int> s;
	int i;
	for(i=0;i<n;i++)
		if(!in[i])
			s.push(i);//所有入度为0的点入栈，如果这些点多于1的话，序列不确定
	num=0;
	flag=0;
	while(!s.empty()){
		if(s.size()>1)
			flag=1; //序列不确定
		t=s.top();
		s.pop();
		list[num++]=t;  //记录出栈的数字
		for(i=0;i<n;i++)
			if(map[t][i])
				if(--in[i]==0)
					s.push(i); //入度为0的点入栈
	}
	if(num!=n)//不能拓扑排序，即有环
		return 1;
	else if(flag==1)//有多种排序方式，不能唯一确定
		return 2;
	return 0;//序列能够被唯一确定
}
int main(int argc, char** argv) {
	int determined,inconsistency;
	int i,j,res;
//	freopen("in.txt","r",stdin);
	char a,b;
	while(scanf("%d%d",&n,&m)&&n||m){
		getchar();
		determined=0;
		inconsistency=0;
		memset(map,0,sizeof(map));
		memset(indegree,0,sizeof(indegree));
		for(i=1;i<=m;i++){
			scanf("%c<%c",&a,&b);
			getchar();
			if(!determined&&!inconsistency){
				if(map[b-'A'][a-'A']==1){
					inconsistency=1;
					printf("Inconsistency found after %d relations.\n",i);
					continue;
				}
				if(map[a-'A'][b-'A']==0){
					map[a-'A'][b-'A']=1;
					indegree[b-'A']++;
				}
				res=toposort(n);
				if(res==0){
					printf("Sorted sequence determined after %d relations: ",i);
					for(j=0;j<n;j++)
						printf("%c",list[j]+'A');
					printf(".\n");
					determined=1;
				}
				else if(res==1){
					inconsistency=1;
					printf("Inconsistency found after %d relations.\n",i);
				}
			}
		}
		if(!determined&&!inconsistency)
			printf("Sorted sequence cannot be determined.\n");
	}
	return 0;
}