Graph painting

#ifdef ONPC
    #define _GLIBCXX_DEBUG
#endif
#include <bits/stdc++.h>

#define char unsigned char
#define rep(i, a, b) for(int i=a; i< (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
#define fi first
#define se second
#define pb push_back

#define LSOne(S) ((S) & -(S))

using namespace std;
// mt19937 rnd(239);
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());

typedef long long C;
typedef complex<C> P;
#define X real()
#define Y imag()

template<class T>
istream& operator>> (istream& is, complex<T>& p) {
    T value;
    is >> value;
    p.real(value);
    is >> value;
    p.imag(value);
    return is;
}

typedef long long ll;
typedef long double ld;

using pi = pair<ll, ll>;
using vi = vector<ll>;
template <class T>
using pq = priority_queue<T>;
template <class T>
using pqg = priority_queue<T, vector<T>, greater<T>>;

int popcnt(int x) { return __builtin_popcount(x); }
int popcnt(ll x) { return __builtin_popcountll(x); }

#define MIN(v) *min_element(all(v))
#define MAX(v) *max_element(all(v))
#define LB(c, x) distance((c).begin(), lower_bound(all(c), (x)))
#define UB(c, x) distance((c).begin(), upper_bound(all(c), (x)))

void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ", "; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? ", " : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifdef DEBUG
#define dbg(x...) cerr << "\e[91m"<<__func__<<":"<<__LINE__<<" [" << #x << "] = ["; _print(x); cerr << "\e[39m" << endl;
#else
#define dbg(x...)
#endif

template<typename S, typename T = S> void chmin(S &s, T t) {s = s < t ? s : t;}
template<typename S, typename T = S> void chmax(S &s, T t) {s = s > t ? s : t;}

const int INF = 1e9; // 10^9 = 1B is < 2^31-1
const ll LLINF = 4e18; // 4*10^18 is < 2^63-1
const double EPS = 1e-9;
const ll MOD = 1e9+7;

const int N=1e5+10;
vector<int> adj[N];
int color[N]; // 0-RED, 1-BLUE
bool vis[N];

int solve() {
    int n,m; std::cin >> n >> m;
    for (int i = 1; i <= n; i++) {
        adj[i].clear();
        color[i]=-1;
        vis[i]=false;
    }


    for (int i = 0; i < m; i++) {
        int a,b; std::cin >> a >> b;
        adj[a].pb(b);
        adj[b].pb(a);
    }


    for (int i = 1; i <= n; i++) {
        if(color[i]!=-1) continue;
        queue<int> q;
        q.push(i);
        color[i]=0;
        
        while(!q.empty()) {
            int curr=q.front();
            q.pop();
            //std::cout << "CURR: " << curr << std::endl;
            if(vis[curr]) {
                //std::cout << "cont" << std::endl;
                continue;
            }
            vis[curr]=true;
            int cntDiff=0, nonSet=0;
            for(auto &w:adj[curr]) {
                if(color[w]!=-1 && color[w]!=color[curr]) cntDiff++;
                else if(color[w]==-1) nonSet++;
            }

            //std::cout << cntDiff << " " << nonSet << " out of " << adj[curr].size() << std::endl;
            //std::cout << "need at least: " << adj[curr].size()/2 << std::endl;
            int todoDiff=max(0, (int)adj[curr].size()/2-cntDiff);
            //std::cout << "need diff still: " << todoDiff << std::endl;
            //assert(nonSet>=todoDiff);
            for(auto &w:adj[curr]) {
                if(color[w]==-1) {
                    if(todoDiff>0) {
                        color[w]=color[curr];
                        todoDiff--;
                    } else {
                        color[w]=1-color[curr];
                    }
                    q.push(w);
                } 
            }
        }
    }

    for (int i = 1; i <= n; i++) {
        std::cout << (color[i] ? "B " : "R ");
    }
    std::cout  << std::endl;

    

    return 0;
}

int32_t main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    int TET = 1;
    cin >> TET;
    for (int i = 1; i <= TET; i++) {
        #ifdef ONPC
            cout << "TEST CASE#" << i << endl;
        #endif
        
        if (solve()) {
            break;
        }

        #ifdef ONPC
            cout << "__________________________" << endl;
        #endif
    }
    #ifdef ONPC
        cerr << endl << "finished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec" << endl;
    #endif
}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: ACCEPTED