luogu P1078 cultural tours dfs floyd

We are currently at the point x, we have gone the path length len. Ready to point i. So from x to i, in just floyd incomplete consider the cultural impact of the premise, the shortest for the mp [x] [i]. From i to t, in just floyd incomplete consider the cultural impact of the premise, the shortest for the mp [i] [t]. If len + mp [x] [t] + mp [x] [i] have been found to be longer than the current optimal ans. Then obviously i from x to this point makes no sense, you can prune up.

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 using namespace std;
 5 const int MAXN = 110;
 6 int ans,n,k,m,s,t;
 7 int c[MAXN],map[MAXN][MAXN],q[MAXN];
 8 bool b[MAXN][MAXN],flag[MAXN];
 9 void dfs(int x,int len)
10 {
11     if(x == t)
12     {
13         ans = min(ans,len);
14         return;
15     }
16     int l,r;
17     for(int i = 1; i <= n; i++)
18         if(!flag[i] && ans - len - map[x][i] > map[i][t])
19         {
20             l = q[0] + 1;
21             q[++q[0]] = i;
22             flag[i] = 1;
23             for(int j = 1; j <= n; j++)
24                 if(!flag[j] && b[c[j]][c[i]])
25                 {
26                     q[++q[0]] = j;
27                     flag[j] = 1;
28                 }
29             r = q[0];
30             dfs(i,len + map[x][i]);
31             for(int j = l; j <= r; j++)
32                 flag[q[j]] = 0;
33             q[0] = l - 1;
34         }
35 }
36 void floyd()
37 {
38     for(int k = 1; k <= n; k++)
39         for(int i = 1; i <= n; i++)
40             if(!b[c[k]][c[i]])
41                 for(int j = 1; j <= n; j++)
42                     if(!b[c[j]][c[k]] && !b[c[j]][c[i]])
43                         if(map[i][j] - map[i][k] > map[k][j])
44                             map[i][j] = map[i][k] + map[k][j];
45 }
46 int main()
47 {
48     scanf("%d%d%d%d%d",&n,&k,&m,&s,&t);
49     for(int i = 1; i <= n; i++)
50         scanf("%d",&c[i]);
51     for(int i = 1; i <= k; i++)
52         for(int j = 1; j <= k; j++)
53             scanf("%d",&b[i][j]);
54     for(int i = 1; i <= k; i++)
55         b[i][i] = 1;
56     if(b[c[t]][c[s]])
57     {
58         printf("-1\n");
59         return 0;
60     }
61     memset(map,0x1f,sizeof(map));
62     int tu,tv,td;
63     for(int i = 1; i <= m; i++)
64     {
65         scanf("%d%d%d",&tu,&tv,&td);
66         map[tu][tv] = map[tv][tu] = td;
67     }
68     for(int i = 1; i <= n; i++)
69         map[i][i] = 0;
70     floyd();
71     for(int i = 1;i <= n;i++)
72         if(i != s && i != t)
73             if(b[c[i]][c[s]] || b[c[t]][c[i]])
74             {
75                 q[++q[0]] = i;
76                 flag[i] = 1;
77             }
78     ans = map[0][0];
79     q[++q[0]] = s;
80     flag[s] = 1;
81     dfs(s,0);
82     if(ans == map[0][0])
83         printf("-1\n");
84     else 
85         printf("%d\n",ans);
86     return 0;
87 }