[luogu]P1262 间谍网络 题解

  1 #include<cmath>
  2 #include<stack>
  3 #include<vector>
  4 #include<cstdio>
  5 #include<cstring>
  6 #include<cstdlib>
  7 #include<iostream>
  8 #include<algorithm>
  9 #define APART puts("----------------------")
 10 #define debug 1
 11 #define FILETEST 1
 12 #define inf 100010
 13 #define ll long long
 14 #define ha 998244353
 15 #define INF 0x7fffffff
 16 #define INF_T 9223372036854775807
 17 #define DEBUG printf("%s %d\n",__FUNCTION__,__LINE__)
 18 
 19 namespace chino{
 20 
 21 inline void setting(){
 22 #if FILETEST
 23     freopen("_test.in", "r", stdin);
 24     freopen("_test.me.out", "w", stdout);
 25 #endif
 26     return;
 27 }
 28 
 29 inline int read(){
 30     char c = getchar(), up = c; int num = 0;
 31     for(; c < '0' || c > '9'; up = c, c = getchar());
 32     for(; c >= '0' && c <= '9'; num = (num << 3) + (num << 1) + (c ^ '0'), c = getchar());
 33     return  up == '-' ? -num : num;
 34 }
 35 
 36 int n, m, o;
 37 int ans;
 38 int cntE, cntR, cntJ, cntT;
 39 int val[inf], root[inf];
 40 int belong[inf], in[inf];
 41 int low[inf], dfn[inf], vis[inf];
 42 int head[inf], rehead[inf];
 43 struct Edge{
 44     int to;
 45     int next;
 46 }e[inf << 1], r[inf << 1];
 47 std::stack <int> S;
 48 std::vector <int> V;
 49 
 50 inline void AddEdge
 51 (int from, int to, int &cntE, int *head, Edge *e){
 52     ++cntE;
 53     e[cntE].to = to;
 54     e[cntE].next = head[from];
 55     head[from] = cntE;
 56     return;
 57 }
 58 
 59 void tarjan(int now){
 60     dfn[now] = low[now] = ++cntJ;
 61     S.push(now), vis[now] = 1;
 62     for(int i = head[now]; i; i = e[i].next){
 63         int to = e[i].to;
 64         if(dfn[to] == 0){
 65             tarjan(to);
 66             low[now] = std::min (low[to], low[now]);
 67         } else if(vis[to])
 68             low[now] = std::min (low[now], dfn[to]);
 69     }
 70     if(dfn[now] == low[now]){
 71         int top = S.top();
 72         while(true){
 73             top = S.top(), S.pop();
 74             belong[top] = now;
 75             vis[top] = 0;
 76             for(int i = head[top]; i; i = e[i].next)
 77                 AddEdge(now, e[i].to, cntR, rehead, r), ++in[e[i].to];
 78             if(top == now)
 79                 break;
 80             val[now] = std::min (val[now], val[top]);
 81         }
 82     }
 83     return;
 84 }
 85 
 86 int DFS(int now, int g, int rooty){
 87     if(vis[now] || (rooty == now && g))
 88         return 0;
 89     if(root[now])
 90         ans -= val[now];
 91     root[now] = !g;
 92     vis[now] = g;
 93     for(int i = head[now]; i; i = e[i].next){
 94         int to = e[i].to;
 95             to = belong[to];
 96         DFS(to, 1, rooty);
 97     }
 98     return 1;
 99 }
100 
101 inline void fail(int point){
102     puts("NO");
103     printf("%d\n", point);
104     exit(0);
105 }
106 
107 inline int main(){
108     n = read();
109     m = read();
110     std::fill(val + 1, val + 1 + n, INF);
111     for(int i = 1; i <= m; i++){
112         int u = read();
113         val[u] = read();
114         V.push_back(u);
115     }
116     o = read();
117     for(int i = 1; i <= o; i++){
118         int u = read();
119         int v = read();
120         AddEdge(u, v, cntE, head, e);
121     }
122     for(int i = 1; i <= n; i++){
123         if(dfn[i] == 0)
124             tarjan(i);
125     }
126     for(int i = 1; i <= n; i++){
127         if(in[i] == 0 && val[i] == INF)
128             fail(i);
129     }
130     memset(vis, 0, sizeof vis);
131     for(unsigned int i = 0; i < V.size(); i++)
132         ans += val[belong[V[i]]] * DFS(belong[V[i]], 0, belong[V[i]]);
133     for(int i = 1; i <= n; i++){
134         if(vis[i] == 0 && val[i] == INF && belong[i] == i)
135             fail(i);
136     }
137     puts("YES");
138     printf("%d\n", ans);
139     return 0;
140 }
141 
142 }//namespace chino
143 
144 int main(){return chino::main();}