Submission #1106336

#	Time	Username	Problem	Language	Result	Execution time	Memory
1106336		CodeLakVN	Cat in a tree (BOI17_catinatree)	C++17	100 / 100	382 ms	37828 KiB

catinatree

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

#define name "main"
#define FOR(i, a, b) for (int i = (a); i <= (b); i++)
#define FOD(i, b, a) for (int i = (b); i >= (a); i--)

template <class U, class V>
    bool maximize(U &x, V y) {
        if (x < y) { x = y; return true; }
        return false;
    }

template <class U, class V>
    bool minimize(U &x, V y) {
        if (x > y) { x = y; return true; }
        return false;
    }

const int INF = 1e9;
const int N = 2e5 + 5;

int numNode, limit;
vector<int> adj[N];
int child[N], centroidParent[N];
bool del[N];

int countChild(int u, int p) {
    child[u] = 1;
    for (int v : adj[u]) {
        if (v == p || del[v]) continue;
        child[u] += countChild(v, u);
    }
    return child[u];
}

int findCentroid(int u, int p, int m) {
    for (int v : adj[u]) {
        if(v == p || del[v]) continue;
        if (child[v] > m / 2) return findCentroid(v, u, m);
    }
    return u;
}


int centroidDecomp(int u) {
    int m = countChild(u, -1);
    u = findCentroid(u, -1, m);
    del[u] = 1;
    for (int v : adj[u]) {
        if (del[v]) continue;
        int x = centroidDecomp(v);
        centroidParent[x] = u;
    }
    return u;
}

int high[N];
int par[20][N];

void dfs(int u) {
    for (int v : adj[u]) {
        if (v == par[0][u]) continue;
        high[v] = high[u] + 1;
        par[0][v] = u;
        dfs(v);
    }
}

void setup() {
    dfs(1);
    FOR(i, 1, 18) FOR(u, 1, numNode)
        par[i][u] = par[i - 1][par[i - 1][u]];
    high[0] = -1;
}

int LCA(int u, int v) {
    if (high[u] < high[v]) swap(u, v);
    FOD(i, 18, 0) if (high[par[i][u]] >= high[v])
        u = par[i][u];
    if (u == v) return u;
    FOD(i, 18, 0) if (par[i][u] != par[i][v]) {
        u = par[i][u];
        v = par[i][v];
    }
    return par[0][u];
}

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

bool cmp(int &x, int &y) {
    return high[x] > high[y];
}

int minDistFromCentroid[N];

int getDistToSet(int u) {
    int curMinDist = INF;
    int centroid = u;
    while (centroid != 0) {
        minimize(curMinDist, dist(centroid, u) + minDistFromCentroid[centroid]);
        centroid = centroidParent[centroid];
    }
    return curMinDist;
}

void addToSet(int u) {
    int centroid = u;
    while (centroid != 0) {
        minimize(minDistFromCentroid[centroid], dist(centroid, u));
        centroid = centroidParent[centroid];
    }
}

int main() {
    ios_base::sync_with_stdio(NULL);
    cin.tie(0); cout.tie(0);
    if (fopen(name".inp", "r")) {
        freopen(name".inp", "r", stdin);
        freopen(name".out", "w", stdout);
    }

    cin >> numNode >> limit;
    FOR(i, 2, numNode) {
        int u;
        cin >> u;
        u++;
        adj[u].push_back(i);
        adj[i].push_back(u);
    }

    int root = centroidDecomp(1);
    centroidParent[root] = 0;

    vector<int> nodes;
    FOR(u, 1, numNode) nodes.push_back(u);
    setup();
    sort(nodes.begin(), nodes.end(), cmp);

    memset(minDistFromCentroid, 0x3f, sizeof(minDistFromCentroid));
    int ans = 0;
    for (int u : nodes) if(getDistToSet(u) >= limit) {

        ans++;
        addToSet(u);
    }

    cout << ans;

    return 0;
}

// Lak lu theo dieu nhac ^.^

Compilation message (stderr)

catinatree.cpp: In function 'int main()':
catinatree.cpp:124:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  124 |         freopen(name".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
catinatree.cpp:125:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  125 |         freopen(name".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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