• BZOJ2199 [Usaco2011 Jan]奶牛议会


    首先建立一个2-SAT的裸模型,然后发现。。。tarjan没法判断'?'的情况

    于是暴力对每一个议案check一下,直接dfs即可

      1 /**************************************************************
      2     Problem: 2199
      3     User: rausen
      4     Language: C++
      5     Result: Accepted
      6     Time:160 ms
      7     Memory:884 kb
      8 ****************************************************************/
      9  
     10 #include <cstdio>
     11 #include <cstring>
     12 #include <algorithm>
     13  
     14 using namespace std;
     15 const char ch[3] = {'?', 'N', 'Y'};
     16 const int N = 2005;
     17 const int M = N << 2;
     18  
     19 struct edge {
     20   int next, to;
     21   edge() {}
     22   edge(int _n, int _t) : next(_n), to(_t) {}
     23 } e[M];
     24  
     25 int n, m;
     26 int first[N], tot;
     27 bool vis[N];
     28 int ans[N];
     29  
     30 int read() {
     31   int x = 0;
     32   char ch = getchar();
     33   while (ch < '0' || '9' < ch)
     34     ch = getchar();
     35   while ('0' <= ch && ch <= '9')
     36     (x *= 10) += ch - '0', ch = getchar();
     37   return x;
     38 }
     39  
     40 int get() {
     41   int x = read();
     42   char ch = getchar();
     43   while (ch != 'Y' && ch != 'N')
     44     ch = getchar();
     45   if (ch == 'Y') --(x <<= 1);
     46   else x <<= 1;
     47   return x;
     48 }
     49  
     50 void add_edge(int x, int y) {
     51   e[++tot] = edge(first[x], y);
     52   first[x] = tot;
     53 }
     54  
     55 #define y e[x].to
     56 void dfs(int p) {
     57   int x;
     58   vis[p] = 1;
     59   for (x = first[p]; x; x = e[x].next)
     60     if (!vis[y]) dfs(y);
     61 }
     62 #undef y
     63  
     64 bool check(int p) {
     65   int i;
     66   memset(vis, 0, sizeof(vis));
     67   dfs(p);
     68   for (i = 1; i <= n; ++i)
     69     if (vis[2 * i] && vis[2 * i - 1]) return 0;
     70   return 1;
     71 }
     72                  
     73  
     74 int main() {
     75   int i, a, b, c, d, p, q;
     76   n = read(), m = read();
     77   for (i = 1; i <= m; ++i) {
     78     a = get(), c = get();
     79     if (a & 1) b = a + 1;
     80     else b = a - 1;
     81     if (c & 1) d = c + 1;
     82     else d = c - 1;
     83     add_edge(b, c);
     84     add_edge(d, a);
     85   }
     86   for (i = 1; i <= n; ++i) {
     87     p = check(2 * i - 1);
     88     q = check(2 * i);
     89     if (!p && !q) {
     90       puts("IMPOSSIBLE");
     91       return 0;
     92     }
     93     else if (p && q) ans[i] = 0;
     94     else if (!p) ans[i]= 1;
     95     else ans[i] = 2;
     96   }
     97   for (i = 1; i <= n; ++i)
     98     putchar(ch[ans[i]]);
     99   puts("");
    100   return 0;
    101 }
    View Code
    By Xs酱~ 转载请说明 博客地址:http://www.cnblogs.com/rausen
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  • 原文地址:https://www.cnblogs.com/rausen/p/4266619.html
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