[luoguP3275] [SCOI2011]糖果（差分约束）

Posted 2020-09-23 蒟蒻zht的博客

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差分约束裸题

但是坑！

有一个点是长为10W的链，需要逆序加边才能过（真是玄学）

还有各种坑爹数据

开longlong

 

——代码

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <iostream>
 4 #define N 200001
 5 
 6 int n, k, cnt;
 7 long long ans, dis[N];
 8 int head[N], to[N << 1], val[N << 1], next[N << 1];
 9 bool vis[N];
10 
11 inline int read()
12 {
13     int x = 0, f = 1;
14     char ch = getchar();
15     for(; !isdigit(ch); ch = getchar()) if(ch == ‘-‘) f = -1;
16     for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - ‘0‘;
17     return x * f;
18 }
19 
20 inline void add(int x, int y, int z)
21 {
22     to[cnt] = y;
23     val[cnt] = z;
24     next[cnt] = head[x];
25     head[x] = cnt++;
26 }
27 
28 inline bool spfa(int u)
29 {
30     int i, v;
31     vis[u] = 1;
32     for(i = head[u]; i ^ -1; i = next[i])
33     {
34         v = to[i];
35         if(dis[v] > dis[u] + val[i])
36         {
37             dis[v] = dis[u] + val[i];
38             if(vis[v]) return 0;
39             else if(!spfa(v)) return 0;
40         }
41     }
42     vis[u] = 0;
43     return 1;
44 }
45 
46 int main()
47 {
48     int i, j, x, y, z;
49     n = read();
50     k = read();
51     memset(head, -1, sizeof(head));
52     for(i = n; i >= 1; i--) add(0, i, -1);
53     for(i = 1; i <= k; i++)
54     {
55         z = read();
56         x = read();
57         y = read();
58         if(z == 1) add(x, y, 0), add(y, x, 0);
59         if(z == 2)
60         {
61             add(x, y, -1);
62             if(x == y)
63             {
64                 puts("-1");
65                 return 0;
66             }
67         }
68         if(z == 3) add(y, x, 0);
69         if(z == 4)
70         {
71             add(y, x, -1);
72             if(x == y)
73             {
74                 puts("-1");
75                 return 0;
76             }
77         }
78         if(z == 5) add(x, y, 0);
79     }
80     if(spfa(0))
81     {
82         for(i = 1; i <= n; i++) ans -= dis[i];
83         printf("%lld\n", ans);
84     }
85     else puts("-1");
86     return 0;
87 } 

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