pku 1094(拓扑排序，多次拓扑)

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/*

  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[N];

char ans[N]; //存拓扑序 

int inDeg[N]; //入度数 

struct node {

    int v;

    node *next;

    node(int vv, node *p) {

        v = vv;

        next = p;

    }

};



struct graph {

    node *link;

}G[N];



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;

}