Submission #588383

#	Time	Username	Problem	Language	Result	Execution time	Memory
588383		79brue	Star Trek (CEOI20_startrek)	C++17	30 / 100	1087 ms	30400 KiB

startrek

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
const ll MOD = 1000000007;

struct Matrix{
    int n, m;
    ll mat[2][2];
    Matrix(){}
    Matrix(int n, int m): n(n), m(m){
        for(int i=0; i<n; i++) for(int j=0; j<m; j++) mat[i][j] = 0;
    }

    Matrix operator*(const Matrix &r)const{
        assert(m == r.n);
        Matrix ret (n, r.m);
        for(int i=0; i<n; i++){
            for(int j=0; j<m; j++){
                for(int k=0; k<r.m; k++){
                    ret.mat[i][k] += mat[i][j] * r.mat[j][k];
                    ret.mat[i][k] %= MOD;
                }
            }
        }
        return ret;
    }
};

ll mpow(ll x, ll y){
    if(!y) return 1;
    if(y%2) return mpow(x, y-1) * x % MOD;
    ll tmp = mpow(x, y/2);
    return tmp*tmp%MOD;
}

Matrix BasicMatrix(int n, int m){
    Matrix mat (n, m);
    assert(n==m);
    for(int i=0; i<n; i++) mat.mat[i][i] = 1;
    return mat;
}

Matrix mpow(Matrix x, ll y){
    if(!y) return BasicMatrix(x.n, x.m);
    if(y&1) return mpow(x, y-1) * x;
    Matrix tmp = mpow(x, y/2);
    return tmp * tmp;
}

ll n;
ll k;
vector<int> link[100002];
ll mat[400002];
int ex[400002], ey[400002];
int parEdge[400002];
bool canWin[400002];
bool dfsChk[400002], findChk[400002][2];

ll group[400002], groupCnt[2];
ll find1[400002][2];
ll res[400002];
ll ans;

void groupDfs(int x, int p=-1){
    groupCnt[group[x]]++;
    for(auto y: link[x]){
        if(ey[y]==p) continue;
        group[ey[y]] = !group[x];
        groupDfs(ey[y], x);
    }
}

bool dfs(int x, int pe){
    if(dfsChk[pe]) return mat[pe];
    dfsChk[pe] = 1;
    for(auto y: link[x]){
        if((y^pe)==1) continue;
        if(!dfs(ey[y], y)) mat[pe] = 1;
    }
    return mat[pe];
}

int dfsFind(int x, int pe, bool dp){ /// 무조건 지나야 하는 상대 차례 점 개수 찾기
    if(findChk[pe][dp]) return find1[pe][dp];
    findChk[pe][dp] = 1;
    if(!dp){ /// my turn
        int cnt = 0;
        for(auto y: link[x]){
            if((y^1)!=pe && !mat[y]) cnt++;
        }
        if(cnt > 1) return find1[pe][dp] = 0;
        assert(cnt == 1);
        for(auto y: link[x]){
            if((y^1)!=pe && !mat[y]) return find1[pe][dp] = dfsFind(ey[y], y, !dp);
        }
        exit(1);
    }
    else{ /// your turn
        int ret = 1;
        for(auto y: link[x]){
            if((y^1)==pe) continue;
            ret += dfsFind(ey[y], y, !dp);
        }
        return find1[pe][dp] = ret;
    }
}

int main(){
    scanf("%lld %lld", &n, &k);
    for(int i=1; i<n; i++){
        int x, y;
        scanf("%d %d", &x, &y);
        link[x].push_back(i*2-2);
        link[y].push_back(i*2-1);
        ex[i*2-2] = x, ey[i*2-2] = y;
        ex[i*2-1] = y, ey[i*2-1] = x;
    }
    for(int i=n; i<n+n; i++){
        ex[i*2-2] = -1, ey[i*2-2] = i-n+1;
        ex[i*2-1] = i-n+1, ey[i*2-1] = -1;
        parEdge[i-n+1] = i*2-2;
    }

    groupDfs(1);
    for(int i=1; i<=n; i++){
        canWin[i] = dfs(i, parEdge[i]);
        if(canWin[i]) res[i] = groupCnt[!group[i]] - dfsFind(i, parEdge[i], 0);
        else res[i] = dfsFind(i, parEdge[i], 1);
    }

    Matrix first (1, 2);
    first.mat[0][0] = first.mat[0][1] = 0;
    for(int i=1; i<=n; i++){
        if(canWin[i]) first.mat[0][0]++;
        else first.mat[0][1]++;
    }

    Matrix multiplier (2, 2); /// 0: WIN, 1: LOSE
    for(int i=1; i<=n; i++){
        if(canWin[i]){
            multiplier.mat[0][0] = (multiplier.mat[0][0] + n) % MOD;
            multiplier.mat[1][0] = (multiplier.mat[1][0] + groupCnt[group[i]]) % MOD;
            multiplier.mat[1][0] = (multiplier.mat[1][0] + find1[i][0]) % MOD;

            multiplier.mat[1][1] = (multiplier.mat[1][1] + n - groupCnt[group[i]] - res[i] + MOD)%MOD;
        }
        else{
            multiplier.mat[1][0] = (multiplier.mat[1][0] + res[i]) % MOD;

            multiplier.mat[0][1] = (multiplier.mat[0][1] + n) % MOD;
            multiplier.mat[1][1] = (multiplier.mat[1][1] + n - res[i]) % MOD;
        }
    }
    multiplier = mpow(multiplier, k-1);
    first = first * multiplier;
    ll Wsum = first.mat[0][0], Lsum = first.mat[0][1];
    ll ans = 0;
    if(canWin[1]){
        ans = (Wsum * n + groupCnt[group[1]] * Lsum + res[1] * Lsum) % MOD;
    }
    else ans = res[1] * Lsum % MOD;

    printf("%lld", ans);
}

Compilation message (stderr)

startrek.cpp: In function 'int main()':
startrek.cpp:111:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  111 |     scanf("%lld %lld", &n, &k);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~
startrek.cpp:114:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  114 |         scanf("%d %d", &x, &y);
      |         ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 0
• Subtask 2: 7 / 7
• Subtask 3: 8 / 8
• Subtask 4: 15 / 15
• Subtask 5: 0 / 15
• Subtask 6: 0 / 20
• Subtask 7: 0 / 20
• Subtask 8: 0 / 15