Submission #231481

#	Time	Username	Problem	Language	Result	Execution time	Memory
231481		rqi	One-Way Streets (CEOI17_oneway)	C++14	100 / 100	231 ms	36856 KiB

oneway

#include <bits/stdc++.h>
using namespace std;
 
typedef long long ll;
typedef long double ld;
typedef double db; 
typedef string str; 

typedef pair<int,int> pi;
typedef pair<ll,ll> pl; 
typedef pair<db,db> pd; 

typedef vector<int> vi; 
typedef vector<ll> vl; 
typedef vector<db> vd; 
typedef vector<str> vs; 
typedef vector<pi> vpi;
typedef vector<pl> vpl; 
typedef vector<pd> vpd; 

#define mp make_pair 
#define f first
#define s second
#define sz(x) (int)x.size()
#define all(x) begin(x), end(x)
#define rall(x) (x).rbegin(), (x).rend() 
#define rsz resize
#define ins insert 
#define ft front() 
#define bk back()
#define pf push_front 
#define pb push_back
#define eb emplace_back 
#define lb lower_bound 
#define ub upper_bound 

#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define trav(a,x) for (auto& a: x)

const int MOD = 1e9+7; // 998244353;
const int MX = 2e5+5; 
const ll INF = 1e18; 
const ld PI = acos((ld)-1);
const int xd[4] = {1,0,-1,0}, yd[4] = {0,1,0,-1}; 

template<class T> bool ckmin(T& a, const T& b) { 
    return b < a ? a = b, 1 : 0; }
template<class T> bool ckmax(T& a, const T& b) { 
    return a < b ? a = b, 1 : 0; } 
int pct(int x) { return __builtin_popcount(x); } 
int bit(int x) { return 31-__builtin_clz(x); } // floor(log2(x)) 
int cdiv(int a, int b) { return a/b+!(a<0||a%b == 0); } // division of a by b rounded up, assumes b > 0 

// INPUT
template<class A> void re(complex<A>& c);
template<class A, class B> void re(pair<A,B>& p);
template<class A> void re(vector<A>& v);
template<class A, size_t SZ> void re(array<A,SZ>& a);

template<class T> void re(T& x) { cin >> x; }
void re(db& d) { str t; re(t); d = stod(t); }
void re(ld& d) { str t; re(t); d = stold(t); }
template<class H, class... T> void re(H& h, T&... t) { re(h); re(t...); }

template<class A> void re(complex<A>& c) { A a,b; re(a,b); c = {a,b}; }
template<class A, class B> void re(pair<A,B>& p) { re(p.f,p.s); }
template<class A> void re(vector<A>& x) { trav(a,x) re(a); }
template<class A, size_t SZ> void re(array<A,SZ>& x) { trav(a,x) re(a); }

// TO_STRING
#define ts to_string
template<class A, class B> str ts(pair<A,B> p);
template<class A> str ts(complex<A> c) { return ts(mp(c.real(),c.imag())); }
str ts(bool b) { return b ? "true" : "false"; }
str ts(char c) { str s = ""; s += c; return s; }
str ts(str s) { return s; }
str ts(const char* s) { return (str)s; }
str ts(vector<bool> v) { 
    bool fst = 1; str res = "{";
    F0R(i,sz(v)) {
        if (!fst) res += ", ";
        fst = 0; res += ts(v[i]);
    }
    res += "}"; return res;
}
template<size_t SZ> str ts(bitset<SZ> b) {
    str res = ""; F0R(i,SZ) res += char('0'+b[i]);
    return res; }
template<class T> str ts(T v) {
    bool fst = 1; str res = "{";
    for (const auto& x: v) {
        if (!fst) res += ", ";
        fst = 0; res += ts(x);
    }
    res += "}"; return res;
}
template<class A, class B> str ts(pair<A,B> p) {
    return "("+ts(p.f)+", "+ts(p.s)+")"; }

// OUTPUT
template<class A> void pr(A x) { cout << ts(x); }
template<class H, class... T> void pr(const H& h, const T&... t) { 
    pr(h); pr(t...); }
void ps() { pr("\n"); } // print w/ spaces
template<class H, class... T> void ps(const H& h, const T&... t) { 
    pr(h); if (sizeof...(t)) pr(" "); ps(t...); }

// DEBUG
void DBG() { cerr << "]" << endl; }
template<class H, class... T> void DBG(H h, T... t) {
    cerr << to_string(h); if (sizeof...(t)) cerr << ", ";
    DBG(t...); }
#ifdef LOCAL // compile with -DLOCAL
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__)
#else
#define dbg(...) 42
#endif

// FILE I/O
void setIn(string s) { freopen(s.c_str(),"r",stdin); }
void setOut(string s) { freopen(s.c_str(),"w",stdout); }
void unsyncIO() { ios_base::sync_with_stdio(0); cin.tie(0); }
void setIO(string s = "") {
    unsyncIO();
    // cin.exceptions(cin.failbit); 
    // throws exception when do smth illegal
    // ex. try to read letter into int
    if (sz(s)) { setIn(s+".in"), setOut(s+".out"); } // for USACO
}

mt19937 rng((uint32_t)chrono::steady_clock::now().time_since_epoch().count()); 


/**
 * Description: Disjoint Set Union with path compression. 
     * Add edges and test connectivity. Use for Kruskal's 
     * minimum spanning tree.
 * Time: O(\alpha(N))
 * Source: CSAcademy, KACTL
 * Verification: USACO superbull
 */

struct DSU {
    vi e; void init(int n) { e = vi(n,-1); }
    int get(int x) { return e[x] < 0 ? x : e[x] = get(e[x]); } 
    bool sameSet(int a, int b) { return get(a) == get(b); }
    int size(int x) { return -e[get(x)]; }
    bool unite(int x, int y) { // union-by-rank
        x = get(x), y = get(y); if (x == y) return 0;
        if (e[x] > e[y]) swap(x,y);
        e[x] += e[y]; e[y] = x; return 1;
    }
};

/**template<class T> T kruskal(int n, vector<pair<T,pi>> ed) {
    sort(all(ed));
    T ans = 0; DSU D; D.init(n+1); // edges that unite are in MST
    trav(a,ed) if (D.unite(a.s.f,a.s.s)) ans += a.f; 
    return ans;
}*/




/**
 * Description: Calculates least common ancestor in tree 
     * with root $R$ using binary jumping. 
 * Time: O(N\log N) build, O(\log N) query
 * Source: USACO Camp
 * Verification: Debug the Bugs
 */

template<int SZ> struct LCA {
    static const int BITS = 32-__builtin_clz(SZ);
    int N = 1, par[BITS][SZ], depth[SZ], mind[SZ][2];
    int ind[SZ]; //index of edge from i to par[i]
    vpi adj[SZ]; 
    /// INITIALIZE
    void ae(int u, int v, int i) { adj[u].pb(mp(v, i)), adj[v].pb(mp(u, i)); }
    void dfs(int u, int prev, int index = 0){
        ind[u] = index;
        par[0][u] = prev; depth[u] = depth[prev]+1;
        trav(v,adj[u]) if (v.f != prev) dfs(v.f, u, v.s);
    }
    void propmind(int node, int prv){
        for(auto u: adj[node]){
            if(u.f == prv) continue;
            propmind(u.f, node);
            for(int j = 0; j < 2; j++){
                ckmin(mind[node][j], mind[u.f][j]);
            }
            
        }
    }

    void init(int _N) {
        N = _N; 
        for(int i = 1; i <= N; i++){
            //dbg(i);
            mind[i][0] = mind[i][1] = MOD;
            if(depth[i] == 0) dfs(i, 0);
        }

        FOR(k,1,BITS) FOR(i,1,N+1) 
            par[k][i] = par[k-1][par[k-1][i]];
    }


    /// QUERY
    int getPar(int a, int b) {
        R0F(k,BITS) if (b&(1<<k)) a = par[k][a];
        return a; }
    int lca(int u, int v){
        if (depth[u] < depth[v]) swap(u,v);
        u = getPar(u,depth[u]-depth[v]);
        R0F(k,BITS) if (par[k][u] != par[k][v]) 
            u = par[k][u], v = par[k][v];
        return u == v ? u : par[0][u];
    }
    int dist(int u, int v) {
        return depth[u]+depth[v]-2*depth[lca(u,v)]; }
};

const int mx = 100005;
int n, m, p;
pi elist[mx];
int dir[mx]; //0 = both, 1 = right, 2 = left
vpi adj[mx];
pi cond[mx];

bool visited[mx];
bool processed[mx];

int dist[mx];
int mindepth[mx];
int par[mx];
vi child[mx];

DSU dsu;
LCA<100105> lca;

void genDFS(int node, int d = 0){
    //dbg(node, d);
    visited[node] = 1;
    dist[node] = d;
    for(auto u: adj[node]){
        if(processed[u.s] == 1) continue;
        processed[u.s] = 1;
        if(visited[u.f] == 1){
            //backedge
            //dbg(node, u.f);
            ckmin(mindepth[node], dist[u.f]);
            continue;
        }
        child[node].pb(u.f);
        par[u.f] = node;
        genDFS(u.f, d+1);
    }
}

void propMinDepth(int node){
    for(auto u: child[node]){
        propMinDepth(u);
        ckmin(mindepth[node], mindepth[u]);
    }
}

int main() {
    setIO();
    //#warning self & double edges?
    //Input
    cin >> n >> m;
    for(int i = 1; i <= m; i++){
        int a, b;
        cin >> a >> b;
        elist[i] = mp(a, b);
        if(a == b) continue; //take care of self edges
        adj[a].pb(mp(b, i));
        adj[b].pb(mp(a, i));
    }

    int p;
    cin >> p;

    for(int i = 1; i <= p; i++){
        int x, y;
        cin >> x >> y;
        cond[i] = mp(x, y);
    }

    //Generate dfs forest with depths & parent. When backedge occurs, put mindepth on that node. 

    for(int i = 1; i <= n; i++) mindepth[i] = MOD;
    for(int i = 1; i <= n; i++){
        if(visited[i] == 1) continue;
        genDFS(i);
    }


    //mindepth of every node becomes min of mindepth of all its children


    for(int i = 1; i <= n; i++){
        if(dist[i] == 0) propMinDepth(i);
    }

    //for(int i = 1; i <= n; i++) dbg(i, mindepth[i]);

    //If mindepth < depth, merge and its parent in the DSU.

    dsu.init(n+5);
    for(int i = 1; i <= n; i++){
        //dbg(i, par[i]);
        if(mindepth[i] < dist[i]){
            //dbg(i, par[i]);
            dsu.unite(i, par[i]);
        }
    }


    //create LCA forest with new edges with dsu.get(), init. Probably change init
    for(int i = 1; i <= m; i++){
        elist[i].f = dsu.get(elist[i].f);
        elist[i].s = dsu.get(elist[i].s);
        int a = elist[i].f;
        int b = elist[i].s;
        if(a != b){
            lca.ae(a, b, i);
            //dbg(a, b, i);
        }
    }

    lca.init(n);



    //Upedges from a to lca, downedges from lca to b.
    
    //for(int i = 1; i <= n; i++) dbg(i, lca.depth[i]);

    for(int i = 1; i <= p; i++){
        pi u = cond[i];
        int a = dsu.get(u.f);
        int b = dsu.get(u.s);
        int c = lca.lca(a, b);
        //dbg(u, a, b, c);
        ckmin(lca.mind[a][0], lca.depth[c]); //up
        ckmin(lca.mind[b][1], lca.depth[c]); //down
        //dbg(a, c);
        //dbg(b, c);
    }


    //mindepth (for up & down) becomes min of mindepth for all its children
    for(int i = 1; i <= n; i++){
        if(lca.depth[i] == 1){
            lca.propmind(i, 0);
        }
    }

    //for(int i = 1; i <= n; i++) dbg(i, lca.mind[i][0], lca.mind[i][1]);
    
    //If mindepth < depth for up/down, direct the edge up/down. 
    for(int i = 1; i <= n; i++){
        int z = lca.ind[i];
        if(z == 0) continue;
        for(int j = 0; j < 2; j++){
            if(lca.mind[i][j] < lca.depth[i]){
                
                int fac = 1;
                if(elist[z].f == i) fac = 0;
                //dbg(i, j, z, elist[z]);
                fac^=j;
                if(fac == 0){
                    dir[z] = 1;
                }
                else dir[z] = 2;
                /*if(elist[z].f == i){
                    //if j == 0, direct it right
                    //if j == 1, direct it left
                }
                else{
                    //if j == 0, direct it left
                    //if j == 1, direct it right
                }*/
            }
        }
    }


    //Go through original edgelist and print
    
    for(int i = 1; i <= m; i++){
        if(dir[i] == 0) cout << 'B';
        else if(dir[i] == 1) cout << 'R';
        else cout << 'L';
    }
    cout << "\n";



    // you should actually read the stuff at the bottom
}

/* stuff you should look for
    * int overflow, array bounds
    * special cases (n=1?)
    * do smth instead of nothing and stay organized
    * WRITE STUFF DOWN
*/

Compilation message (stderr)

oneway.cpp: In function 'void setIn(std::__cxx11::string)':
oneway.cpp:123:31: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
 void setIn(string s) { freopen(s.c_str(),"r",stdin); }
                        ~~~~~~~^~~~~~~~~~~~~~~~~~~~~
oneway.cpp: In function 'void setOut(std::__cxx11::string)':
oneway.cpp:124:32: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
 void setOut(string s) { freopen(s.c_str(),"w",stdout); }
                         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 30 / 30
• Subtask 2: 30 / 30
• Subtask 3: 40 / 40