uva1391 2-SAT 问题

#include <iostream>
#include <algorithm>
#include <string.h>
#include <cstdio>
#include <vector>
using namespace std;
const int maxn=100000+10;
struct TwoSAT{
   int n;
   vector<int > G[maxn*2];
   bool mark[maxn*2];
   int S[maxn*2],c;
   bool dfs(int x){
       if(mark[x^1]) return false;
       if(mark[x]) return true;
       mark[x]=true;
       S[c++]=x;
       for(int i=0; i<G[x].size(); i++)
         if(!dfs(G[x][i])) return false;
       return true;
   }
   void inti(int n){
       this->n =n;
       for(int i=0; i<2*n; ++i)
        G[i].clear();
       memset(mark,0,sizeof(mark));
   }
   void add_clause(int x, int xval, int y, int yval){
        x = x * 2 + xval;
        y = y * 2 + yval;
        G[x^1].push_back(y);
        G[y^1].push_back(x);
   }
   bool solve(){
      for(int i=0; i<n*2; i+=2 )
      if(!mark[i] && !mark[i+1]){
        c=0;
        if(!dfs(i)){
            while(c>0) mark[ S[ --c ] ] = false;
            if(!dfs(i+1)) return false;
        }
      }
      return true;
   }
}solver;
int n,m,total_age;
int age[maxn];
bool isyoung(int x){
    return x*n<total_age;
}
int main()
{
    while(scanf("%d%d",&n,&m)==2&&n){
          total_age=0;

          for(int i=0; i<n; ++i){
            scanf("%d",&age[i]);
             total_age+=age[i];
            }

           solver.inti(n);
          for(int i=0; i<m; ++i){
              int u,v;
              scanf("%d%d",&u,&v); u--; v--;
              if(u==v)continue;
              solver.add_clause(u, 1 , v ,  1);
              if(isyoung(age[u])==isyoung(age[v])){
                  solver.add_clause( u, 0 , v ,0 );
              }
          }
          if(!solver.solve()) printf("No solution.\n");
          else {

             for(int i=0; i<n; i++)
                if(solver.mark[i*2]) printf("C\n");
                else if(isyoung(age[i])) printf("B\n");
                else printf("A\n");
          }
    }

    return 0;
}