UVA Live 3713 Astronauts （2-SAT）

#include<bits/stdc++.h>
using namespace std;
const int maxn = 1e5+5;

#define PB push_back
bool vis[maxn*2];
vector<int> G[maxn*2];
int N,S[maxn*2],top;
void initGraph(int n)
{
N = n*2;
for(int i = 0; i < N; i++) G[i].clear();
memset(vis,0,sizeof(bool)*(n<<1|1));
}

bool dfs(int x)
{
if(vis[x^1]) return false;
if(vis[x]) return true;
vis[x] = true;
S[top++] = x;
for(int i = 0; i < (int)G[x].size(); i++){
if(!dfs(G[x][i])) return false;
}
return true;
}

bool twoSAT()
{
for(int i = 0; i < N; i+=2){
if(!vis[i]&&!vis[i^1]){
top = 0;
if(!dfs(i)){
while(top>0) vis[S[--top]] = false;
if(!dfs(i^1)) return false;
}
}
}
return true;
}

void add_clause(int x,int xv,int y,int yv)
{
x = x<<1|xv;
y = y<<1|yv;
G[x^1].PB(y);
G[y^1].PB(x);
}

int tp[maxn];
int age[maxn];
char bin[2][2] = {{'C','B'},{'C','A'}};

int main()
{
//freopen("in.txt","r",stdin);
int n,m;
while(scanf("%d%d",&n,&m),n){
int sum = 0;
for(int i = 0; i < n; i++){
scanf("%d",age+i);
sum += age[i];
}
for(int i = 0; i < n; i++){
if(age[i]*n >= sum) tp[i] = 1;
else tp[i] = 0;
}
initGraph(n);
for(int i = 0; i < m; i++){
int u,v; scanf("%d%d",&u,&v);
if(tp[--u]^tp[--v]){
add_clause(u,1,v,1);
}else {
add_clause(u,0,v,0);
add_clause(u,1,v,1);
}
}
if(twoSAT()){
for(int i = 0; i < N; i+=2){
putchar(bin[tp[i>>1]][vis[i^1]]);
putchar('\n');
}
}else {
puts("No solution.");
}
}
return 0;
}