【差分约束】SCOI2011糖果

P3275 [SCOI2011]糖果

快noip了我还在干什么啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊

来我们看这道题

根据条件建图，因为求得是最小值，所以要跑最长路qwq（这是我记住的QAQ

不想写了让我们直接看看题解吧！

P3275 [SCOI2011]糖果（five20的题解）

有环代表条件冲突，输出“-1”

建源点的时候反向建会快（这就很妙了

 1 #include<queue>
 2 #include<cstdio>
 3 #include<cstdlib>
 4 #include<iostream>
 5 #define ri register int
 6 #define ll long long
 7 using namespace std;
 8 const int sz = 200010;
 9 int n, k, num = 0;
10 ll ans;
11 int head[sz], dis[sz], tot[sz];
12 bool flag;
13 bool vis[sz];
14 struct edge {
15     int nxt, to, dis;
16 }e[sz << 1];
17 inline int read() {
18     char ch = getchar(); int x = 0, f = 1;
19     while(ch > '9' || ch < '0') {if(ch == '-') f = -1; ch = getchar();}
20     while(ch >= '0' && ch <= '9') {x = x * 10 + ch - '0' ; ch = getchar();}
21     return x * f;
22 }
23 void add(int from, int to, int dis) {
24     e[++num].nxt = head[from];
25     e[num].to = to;
26     e[num].dis = dis;
27     head[from] = num;
28 }
29 void spfa() {
30     queue<int>q;
31     q.push(0);
32     vis[0] = 1;
33     while(!q.empty()) {
34         int u = q.front();
35         q.pop();
36         if(tot[u] == n - 1) {
37             printf("-1");
38             exit(0);
39         }
40         vis[u] = 0;
41         tot[u]++;
42         for(ri i = head[u]; i; i = e[i].nxt) {
43             int v = e[i].to;
44             if(dis[v] < dis[u] + e[i].dis) {
45                 dis[v] = dis[u] + e[i].dis;
46                 if(!vis[v]) {
47                     vis[v] = 1;
48                     q.push(v);
49                 }
50             }
51         }
52     }
53 }
54 int main() {
55     scanf("%d%d", &n, &k);
56     for(ri i = 1; i <= k; i++) {
57         int opt = read(), u = read(), v = read();
58         if(opt == 1) {
59             add(v, u, 0);
60             add(u, v, 0);
61         }
62         else if(opt == 2) {
63             if(u == v) {
64                 flag = 1;
65                 break;
66             }
67             else add(u, v, 1);
68         }
69         else if(opt == 3) add(v, u, 0);
70         else if(opt == 4) {
71             if(u == v) {
72                 flag = 1;
73                 break;
74             }
75             else add(v, u, 1);
76         }
77         else if(opt == 5) add(u, v, 0);
78      }
79      if(flag == 1) {
80          printf("-1");
81          return 0;
82      }
83      for(ri i = n; i >= 1; i--) add(0, i, 1);
84      spfa();
85      for(ri i = 1; i <= n; i++) 
86          ans += dis[i];
87      printf("%lld", ans);
88     return 0;
89 }
90 /*
91 4 7
92 1 3 2
93 2 2 4
94 5 1 3
95 3 4 2
96 3 2 3
97 4 3 1
98 5 1 4
99 */