【POJ 1094】Sorting It All Out

【POJ 1094】Sorting It All Out

拓扑排序

输出第一次成功排序的位置及顺序(能顺利拓扑并在拓扑中不存在同级)

或者

第一个出现与之前给出条件相悖的位置(拓扑过程中出现间断)

坑点是出现任何一种情况就out

代码如下

#include <iostream>

using namespace std;

int in[26],inn[26],n;
int mp[26][26];

int Topo(int op)
{
    int i,j,k,f = 1;
    for(i = 0; i < n; ++i)
        inn[i] = in[i];
    for(i = 0; i < n; ++i)
    {
        k = -1;
        for(j = 0; j < n; ++j)
        {
            if(!inn[j])
            {
                if(k != -1) f = 0;
                k = j;
            }
        }
        j = k;
        if(j == -1) return -1;
        if(op) putchar(‘A‘+j);
        inn[j]--;
        for(k = 0; k < n; ++k)
            inn[k] -= mp[j][k];
    }
    if(op)
        puts(".");
    return f;
}

int main()
{
//    freopen("in.txt","r",stdin);
//    freopen("out.txt","w",stdout);
    int f,m,i,a,b,x;
    char st[5];
    while(~scanf("%d %d",&n,&m) && n && m)
    {
        memset(mp,0,sizeof(mp));
        memset(in,0,sizeof(in));
        f = 0;
        x = -1;
        for(i = 1; i <= m; ++i)
        {
            scanf("%s",st);
            a = st[0]-‘A‘;
            b = st[2]-‘A‘;
            if(st[1] == ‘>‘)
            {
                a += b;
                b = a-b;
                a -= b;
            }
            if(f) continue;
            mp[a][b]++;
            in[b]++;
            f = Topo(0);
            x = i;
        }
        if(!f) puts("Sorted sequence cannot be determined.");
        else if(f == -1) printf("Inconsistency found after %d relations.\n",x);
        else
        {
            printf("Sorted sequence determined after %d relations: ",x);
            Topo(1);
        }
    }
    return 0;
}

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