HDU1814 Peaceful Commission 2SAT

http://acm.hdu.edu.cn/showproblem.php?pid=1814

输出最小字典序。

#include<bits/stdc++.h> 
const int MAXN = 20020; 
const int MAXM = 100010;
using namespace std; 
struct Edge {
     int to,next; 
}edge[MAXM]; 
int head[MAXN],tot; 
void init(){ 
    tot = 0;    
    memset(head,-1,sizeof(head)); 
}  
void addedge(int u,int v){
    edge[tot].to = v;
    edge[tot].next = head[u];
    head[u] = tot++; 
} bool vis[MAXN];//è&#190;é&#171;±ê&#188;&#199;￡&#172;&#206;atrue±íê&#190;&#209;&#161;&#212;&#241; 
int S[MAXN],top;//&#213;&#187; 
bool dfs(int u){
    if(vis[u^1])return false;
    if(vis[u])return true;     
    vis[u] = true;     
    S[top++] = u;     
    for(int i = head[u];i != -1;i = edge[i].next)
        if(!dfs(edge[i].to))    
            return false;    
    return true; 
}
bool Twosat(int n){ 
    memset(vis,false,sizeof(vis));   
    for(int i = 0;i < n;i += 2){        
         if(vis[i] || vis[i^1])
            continue;        
        top = 0;  
        if(!dfs(i)){       
            while(top)
                vis[S[--top]] = false;   
            if(!dfs(i^1)) return false;         
        }     
    }     
    return true; 
} 
int main(){     
    int n,m;   
    int u,v;   
    while(scanf("%d%d",&n,&m) == 2){ 
        init();  
           while(m--){      
            scanf("%d%d",&u,&v);         
            u--;v--;      
            addedge(u,v^1);  
            addedge(v,u^1);         
        }      
        if(Twosat(2*n)){  
            for(int i = 0;i < 2*n;i++) 
                if(vis[i]) 
                   printf("%d
",i+1);       
        }  
        else printf("NIE
");     
    }    
    return 0; 
}