Submission #1112952

#	Time	Username	Problem	Language	Result	Execution time	Memory
1112952		ljtunas	Cat in a tree (BOI17_catinatree)	C++14	100 / 100	341 ms	64716 KiB

catinatree

// author : anhtun_hi , nqg
#include <bits/stdc++.h>
#define ll long long
#define ii pair<ll, ll>
#define fi first
#define se second
#define all(x) x.begin(), x.end()
#define reset(h, v)    memset(h, v, sizeof h)
#define Forv(i, a)     for(auto& i : a)
#define For(i, a, b)   for(int i = a; i <= b; ++i)
#define Ford(i, a, b)  for(int i = a; i >= b; --i)
#define c_bit(i)     __builtin_popcountll(i)
#define Bit(mask, i)    ((mask >> i) & 1LL)
#define onbit(mask, i)  ((mask) bitor (1LL << i))
#define offbit(mask, i) ((mask) &~ (1LL << i))
#define TIME (1.0 * clock() / CLOCKS_PER_SEC)
using namespace std;
namespace std {
    template <typename T, int D>
    struct _vector : public vector <_vector <T, D - 1>> {
        static_assert(D >= 1, "Dimension must be positive!");
        template <typename... Args>
        _vector(int n = 0, Args... args) : vector <_vector <T, D - 1>> (n, _vector <T, D - 1> (args...)) {}
    };
    template <typename T> struct _vector <T, 1> : public vector <T> {
        _vector(int n = 0, const T& val = T()) : vector <T> (n, val) {}
    };
    template <class A, class B> bool minimize(A &a, B b){return a > b ? a = b, true : false;}
    template <class A, class B> bool maximize(A &a, B b){return a < b ? a = b, true : false;}
}
const int dx[] = {0, 0, +1, -1}, dy[] = {-1, +1, 0, 0}, LOG = 20, base = 311, inf = 1e9 + 5;
const int MAXN = 1e6 + 5;
const  ll  mod = 1e9 + 7;
const  ll   oo = 1e18;

//#define int long long

int n, d, sz[MAXN], del[MAXN], dep[MAXN]; vector<int> g[MAXN];

int p[MAXN][22], dad[MAXN];

void dfs(int u, int par) {
    p[u][0] = par;
    For(k, 1, 20) p[u][k] = p[p[u][k - 1]][k - 1];
    for(int v : g[u]) {
        if (v == par) continue;
        dep[v] = dep[u] + 1;
        dfs(v, u);
    }
}

int getlca(int u, int v) {
    if (dep[u] < dep[v]) swap(u, v);
    int len = dep[u] - dep[v];
    For(k, 0, 20) if (Bit(len, k)) u = p[u][k];
    if (u == v) return u;
    Ford(k, 20, 0) if (p[u][k] != p[v][k])
        u = p[u][k], v = p[v][k];
    return p[u][0];
}

int dist(int u, int v) {
    return dep[u] + dep[v] - 2 * dep[getlca(u, v)];
}

void dfsSize(int u, int par){
    sz[u] = 1;
    Forv(v, g[u]) if(v != par && !del[v]) dfsSize(v, u), sz[u] += sz[v];
}

int find(int u, int par, int n){
    Forv(v, g[u]) if(v != par && !del[v] && sz[v] > n / 2) return find(v, u, n);
    return u;
}

void buildCentroid(int u, int par){
    dfsSize(u, 0);
    int centroid = find(u, 0, sz[u]);
    del[centroid] = true;
    dad[centroid] = par;
    Forv(v, g[centroid]) if(v != par && !del[v]) buildCentroid(v, centroid);
}

int mn[MAXN];

int get(int u){
    int res = inf, v = u;
    while(v){
        minimize(res, mn[v] + dist(u, v));
        v = dad[v];
    }
    return res;
}

void update(int u){
    int v = u;
    while(v){
        minimize(mn[v], dist(u, v));
        v = dad[v];
    }
}

void Solve() {
    cin >> n >> d;
    For(i, 2, n){
        int p; cin >> p; ++p;
        g[p].push_back(i);
        g[i].push_back(p);
    }
    buildCentroid(1, 0);
    dfs(1, 0);
    fill(mn, mn + n + 1, inf);
    vector<int> List;
    For(i, 1, n) List.push_back(i);
    sort(all(List), [&](int u, int v){
        return dep[u] > dep[v];
    });
    int ans = 0;
    Forv(i, List) if(get(i) >= d) ++ans, update(i);
    cout << ans << '\n';
}

signed main() {
    cin.tie(0) -> sync_with_stdio(0);
    if(fopen("BOI17_catinatree.inp", "r")) {
        freopen("BOI17_catinatree.inp", "r", stdin);
        freopen("BOI17_catinatree.out", "w", stdout);
    }

    int t = 1;
//    cin >> t;
    while(t --) Solve();

    return 0;
}

Compilation message (stderr)

catinatree.cpp: In function 'int main()':
catinatree.cpp:126:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  126 |         freopen("BOI17_catinatree.inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
catinatree.cpp:127:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  127 |         freopen("BOI17_catinatree.out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 11 / 11
• Subtask 2: 40 / 40
• Subtask 3: 49 / 49