codeforces 468B 2-sat

今天明白了2-SAT;

表示对一对整数之间的关系是否存在

#include<cstdio>
#include<algorithm>
#include<iostream>
#include<cstring>
#include<map>
using namespace std;
const int Maxn = 1e5+10;
int mark[Maxn  << 1];
int s[Maxn * 2],top,tp;
int head[Maxn*2];
map <int,int> mp;
int x[Maxn * 2];
struct  {
    int v,next;
}E[Maxn << 2];
void init(){
    memset(head,-1,sizeof(head));
    memset(E,-1,sizeof(E));
    tp = 0;
}
int n,m,a,b;
void addedge(int u,int v){
    E[tp].v = v;
    E[tp].next = head[u];
    head[u] = tp++;
}
bool dfs(int x){
    if(mark[x^1])return false;
    if(mark[x])return true;
    mark[x] = true;
    s[top++] = x;
    for(int i=head[x];i!=-1;i=E[i].next){
        int v = E[i].v;
        if(!dfs(v))return false;
    }
    return true;
}
bool solve(){
    for(int i=0;i<n*2;i+=2){
        if(!mark[i] && !mark[i+1]){
            top = 0;
            if(!dfs(i)){
                while(top > 0)mark[s[--top]] = false;
                if(!dfs(i+1)) return false;
            }
        }
    }
    return true;
}
int main(){

    init();
    cin >> n >> a >> b;
    for(int i = 1;i<= n;i++){
        scanf("%d",&x[i]);
        mp[x[i]] = i;
    }
    for(int i=1;i<=n;i++){
        int val = x[i],s = i;
        s--;
        int t = mp[a - val];t--;
        if(!mp[a-val])addedge(2*s,2*s+1);
        else {
            addedge(2*s,2*t);
            addedge(2*t+1,2*s+1);
        }
         t=mp[b-val]; t--;
            if(!mp[b-val])
                addedge(2*s+1,2*s);
            else{
                addedge(2*s+1,2*t+1);
                addedge(2*t,2*s);
            }
    }
    if(!solve()){
        puts("NO");
    }
    else {
        printf("YES\n");
        for(int i=0;i<2*n;i+=2){
            if(i!=0)
                printf(" ");
            if(mark[i])
                printf("0");
            else
                printf("1");
        }
        printf("\n");
    }
}