CF1093D Beautiful Graph

思路：

题目倒是没啥好说的，就是注意memset的效率问题。如果循环多次调用memset去初始化一个比较大的数组，那就会很费时间。就是因为这个被hack了。:(

实现：

 #include <bits/stdc++.h>
 using namespace std;
 typedef long long ll;

 const int MOD = ;
 const int MAXN = ;

 vector<int> G[MAXN];
 int col[MAXN];
 int n, m;
 ll c1 = , c2 = , bin[MAXN];

 bool dfs(int v, int c)
 {
     col[v] = c;
     if (c == ) c1++;
     else c2++;
     for (int i = ; i < G[v].size(); i++)
     {
         if (col[G[v][i]] == c) return false;
         if (col[G[v][i]] ==  && !dfs(G[v][i],  - c)) return false;
     }
     return true;
 }

 int main()
 {
     bin[] = ;
     for (int i = ; i <= ; i++) bin[i] = bin[i - ] *  % MOD;
     int t, v, u;
     scanf("%d", &t);
     while (t--)
     {
         scanf("%d%d", &n, &m);
         for (int i = ; i <= n; i++) { G[i].clear(); col[i] = ; }
         for (int i = ; i < m; i++)
         {
             scanf("%d%d", &u, &v);
             G[u].push_back(v);
             G[v].push_back(u);
         }
         bool flg = true;
         ll ans = ;
         for (int i = ; i <= n; i++)
         {
             if (col[i]) continue;
             ll tmp = ; c1 = c2 = ;
             if (!dfs(i, )) { flg = false; break; }
             tmp = (bin[c1] + bin[c2]) % MOD;
             ans = ans * tmp % MOD;
         }
         if (!flg) puts("");
         else printf("%lld\n", ans);
     }
     return ;
 }