POJ 1094 Sorting It All Out(拓扑排序）

题目链接

其实我不懂拓扑排序啊。。。看了DISCUSS，需要判断是不是有环，我傻呼呼的写了个DFS。。。拓扑排序没学好啊。。

  1 #include <iostream>

  2 #include <cstdio>

  3 #include <cstring>

  4 #include <cmath>

  5 #include <algorithm>

  6 using namespace std;

  7 char str[10001][4],ch[31];

  8 int in[50],out[50],o[301],in2[50],out2[50],z[27];

  9 int p[51][51],n,p2[51][51],flag;

 10 int judge()

 11 {

 12     int i,j,num,t,t2;

 13     for(i = 1; i <= n; i ++)

 14     {

 15         in2[i] = in[i];

 16         out2[i] = out[i];

 17     }

 18     for(i = 1; i <= n; i ++)

 19     {

 20         for(j = 1; j <= n; j ++)

 21             p2[i][j] = p[i][j];

 22     }

 23     flag = 0;

 24     for(i = 1; i <= n; i ++)

 25     {

 26         num = 0;

 27         for(j = 1; j <= n; j ++)

 28         {

 29             if(in2[j] == 0)

 30             {

 31                 num ++;

 32                 t = j;

 33             }

 34             else if(in2[j])

 35             {

 36                 t2 = j;

 37             }

 38         }

 39         if(num > 1)

 40             flag = 1;

 41         if(num == 0)

 42             return 0;

 43         for(j = 65; j <= 90; j ++)

 44         {

 45             if(o[j] == t)

 46             {

 47                 ch[i-1] = j;

 48                 break;

 49             }

 50         }

 51         in2[t] = -1;

 52         for(j = 1; j <= 26; j ++)

 53         {

 54             if(p2[t][j])

 55             {

 56                 in2[j] --;

 57                 p2[t][j] = 0;

 58             }

 59         }

 60     }

 61     if(flag) return 2;

 62     ch[n] = '\0';

 63     return 1;

 64 }

 65 int main()

 66 {

 67     int m,i,t1,t2,num;

 68     while(scanf("%d%d",&n,&m)!=EOF)

 69     {

 70         if(!n&&!m) break;

 71         memset(in,0,sizeof(in));

 72         memset(out,0,sizeof(out));

 73         memset(p,0,sizeof(p));

 74         memset(o,0,sizeof(o));

 75         for(i = 1; i <= m; i ++)

 76             scanf("%s",str[i]);

 77         num = 1;

 78         for(i = 1; i <= m; i ++)

 79         {

 80             t1 = str[i][0];

 81             t2 = str[i][2];

 82             if(!o[t1])

 83             {

 84                 o[t1] = num ++;

 85             }

 86             if(!o[t2])

 87             {

 88                 o[t2] = num ++;

 89             }

 90         }

 91         for(i = 1; i <= m; i ++)

 92         {

 93             t1 = str[i][0];

 94             t2 = str[i][2];

 95             p[o[t1]][o[t2]] = 1;

 96             out[o[t1]] ++;

 97             in[o[t2]] ++;

 98             if(judge() == 1)

 99             {

100                 printf("Sorted sequence determined after %d relations: %s.\n",i,ch);

101                 break;

102             }

103             else if(judge() == 0)

104             {

105                 printf("Inconsistency found after %d relations.\n",i);

106                 break;

107             }

108         }

109         if(i == m+1)

110             printf("Sorted sequence cannot be determined.\n");

111     }

112     return 0;

113 }