poj 1094 Sorting It All Out

http://poj.org/problem?id=1094

感觉还是挺好的一个题的，虽说是看的小媛的思路；

题意：判断给出的一些字母的先后顺序，进行拓扑排序，看看是否有序；

思路：用flord判断环还是挺好的，然后拓扑排序判断序列的排序关系；

代码：

View Code

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cstdlib>
using namespace std;
int n = 0;
int m = 0;
int map[30][30] = {0};
int flag = 0;
int huan()
{
    for(int i = 0;i < n; ++i)
    for(int j = 0;j < n; ++j)
    for(int k = 0;k < n; ++k)
    if(map[j][i]&&map[i][k])
    map[j][k] = 1;
    for(int i = 0;i < n; ++i)
    if(map[i][i])
    return 1;
    return 0;
}
int find(int u)
{
    int visit[30] = {0};
    int in[30] = {0};
    char ans[30] = {0};
    for(int i = 0;i < n; ++i)
    for(int j = 0;j < n; ++j)
    if(map[i][j])
    ++in[j];
    int q = 0;
    for(int i = 0;i < n;++i)
    {
        int num = 0;
        int temp  = 0;
        for(int j = 0;j < n; ++j)
        if(!visit[j] && in[j] == 0)
        {
            ans[q++] = j + 'A';
            ++num;
            visit[j] = 1;
            temp = j;
        }
        if(num > 1)
        return 0;
        for(int k = 0;k < n; ++k)
        if(map[temp][k])
        --in[k];
    }
    printf("Sorted sequence determined after %d relations: ",u);
    for(int i = 0;i < q; ++i)
    printf("%c",ans[i]);
    printf(".\n");
    return 1;
}
int main()
{
    while(scanf("%d%d",&n,&m),n&&m)
    {
        memset(map,0,sizeof(map));
        char str[4] = {NULL};
        flag = 0;
        for(int i  = 1;i <= m; ++i)
        {
            scanf("%s",str);
            map[str[0]-'A'][str[2]-'A'] = 1;
            if(flag)
            continue;
            if(huan())
            {
                flag = 1;
                printf("Inconsistency found after %d relations.\n",i);
                continue;
            }
            if(find(i))
            {
                flag = 2;
                continue;
            }
        }
        if(flag == 0)
        printf("Sorted sequence cannot be determined.\n");
    }
}