pku 1094(拓扑排序，多次拓扑)

/*
Name: 拓扑排序，多次拓扑
Copyright:
Author: Try86
Date: 16/04/12 21:36
Description:
*/

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>

using namespace std;

const int N = 27;

bool ch
;
char ans
; //存拓扑序
int inDeg
; //入度数
struct node {
int v;
node *next;
node(int vv, node *p) {
v = vv;
next = p;
}
};

struct graph {
node *link;
}G
;

void init(int n) {
for (int i=0; i<n; ++i) G[i].link = NULL;
return ;
}

void buildG(int u, int v) {
node *p = new node(v, G[u].link);
G[u].link = p;
return ;
}

int topoSort(int n, int s) {
int temp[27], cs, j, k = 0;
for (int i=0; i<n; ++i) temp[i] = inDeg[i];//当前各点入度数
bool flag = true;
while (s--) {
cs = 0;//统计入度为0的顶点个数
for (int i=0; i<n; ++i) {
if (temp[i] == 0) j = i, ++cs;
}
if (cs >= 1) {
if (cs > 1) flag = false;//入度为0的顶点个数大于1，拓扑序有多个，不能比较拓扑序的关系
for (node *p=G[j].link; p; p=p->next) --temp[p->v];
ans[k++] = j + 'A';
temp[j] = -1;
ans[k] = '\0';
}
else return -1;//入度为0的个数为0，存在回路，不能形成拓扑序
}
if (flag) return k;
return 0;
}

void del(node *p) {
if (!p) return ;
del(p->next);
delete p;
return ;
}

int main() {
int n, m;
char str[4];
while (scanf("%d%d", &n, &m) && n+m) {
init(n);
memset(ch, false, sizeof(ch));
memset(inDeg, 0, sizeof(inDeg));
int  junge, counts, k;
junge = counts = 0;
for (int i=0; i<m; ++i) {
scanf ("%s", str);
if (junge != -1) {//junge!=-1,则当前输入下，不存在回路
int u = str[0] - 'A';
int v = str[2] - 'A';
buildG(u, v);
++inDeg[v];
if (!ch[u]) ++counts, ch[u] = true;
if (!ch[v]) ++counts, ch[v] = true;
}
if (junge == 0) {//junge==0,则当前输入下，不存在回路，也不存在孤立点，图连通，需继续拓扑
int t = topoSort(n, counts);
if (t == -1) junge = -1, k = i + 1;
else if (t == n) junge = 1, k = i + 1;
}
}
if (junge == -1) printf ("Inconsistency found after %d relations.\n", k);
else if (junge == 0) printf ("Sorted sequence cannot be determined.\n");
else printf ("Sorted sequence determined after %d relations: %s.\n", k, ans);
for (int i=0; i<n; ++i) del(G[i].link);
}
return 0;
}