Submission #883914

#	Time	Username	Problem	Language	Result	Execution time	Memory
883914		chanhchuong123	Lampice (COCI19_lampice)	C++14	110 / 110	1923 ms	14456 KiB

lampice

#include <bits/stdc++.h>
using namespace std;
#define task ""
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()

const int MOD = 1e9 + 7;
const int MAX = 50005;
const int BASE = 256;
int n;
int len;
char cc;
int maxH;
int sz[MAX];
char a[MAX];
int pw[MAX];
bool rem[MAX];
vector<int> adj[MAX];
unordered_map<int, bool> mp[MAX];

int dfsSZ(int u, int p) {
    sz[u] = 1;
    for (int v: adj[u]) if (v != p && !rem[v]) {
        sz[u] += dfsSZ(v, u);
    }
    return sz[u];
}

int findCentroid(int u, int p, int n) {
    for (int v: adj[u]) if (v != p && !rem[v]) {
        if ((sz[v] << 1) > n)
            return findCentroid(v, u, n);
    }
    return u;
}

void dfs(int u, int p, bool upd, int h, int up, int dw, bool &found) {
    up = (1LL * up * BASE + (a[u] - 'a' + 1)) % MOD; dw = (dw + 1LL * pw[h - 1] * (a[u] - 'a' + 1)) % MOD;
    int value = (1LL * pw[len - h] * dw - up + MOD) % MOD;
    if (upd) mp[h][value] = true;
    else {
        if (h + 1 == len && (1LL * dw * BASE + (cc - 'a' + 1)) % MOD == up) {
            found = true;
            return;
        }
        if (len > h && mp[len - h - 1].find(value) != mp[len - h - 1].end()) {
            found = true;
            return;
        }
    }
    if (h < len) {
        for (int v: adj[u]) if (v != p && !rem[v]) {
            dfs(v, u, upd, h + 1, up, dw, found);
            maxH = max(maxH, h + 1);
            if (found) return;
        }
    }
}

void solve(int u, int p, bool &found) {
    int c = findCentroid(u, p, dfsSZ(u, p)); rem[c] = true;

    maxH = 1;
    cc = a[c];
    for (int v: adj[c]) if (v != p && !rem[v]) {
        dfs(v, c, 0, 1, a[c] - 'a' + 1, 0, found);
        if (found) return;
        dfs(v, c, 1, 1, a[c] - 'a' + 1, 0, found);
    }
    for (int i = 0; i <= maxH; ++i) {
        mp[i].clear();
    }

    for (int v: adj[c]) if (v != p && !rem[v]) {
        solve(v, u, found);
        if (found) return;
    }
}

bool ok(int x) {
    for (int i = 0; i <= n; ++i) mp[i].clear();
    memset(rem, false, sizeof rem);
    bool found = false; len = x;
    solve(1, -1, found);
    return found;
}

int main() {
	ios_base::sync_with_stdio(false); cin.tie(nullptr);

	if (fopen(task".inp", "r")) {
		freopen(task".inp", "r",  stdin);
		freopen(task".out", "w", stdout);
	}

    cin >> n;
    cin >> (a + 1);
    for (int i = 1; i < n; ++i) {
        int u, v; cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    pw[0] = 1; for (int i = 1; i <= n; ++i) {
      pw[i] = 1LL * pw[i - 1] * BASE % MOD;
    }
    int ans = 1;
    for (int i = 0; i < 2; ++i) {
        int l = 0, r = n / 2 + 1;
        while (r - l > 1) {
            int mid = l + r >> 1;
            if (ok(i + 2 * mid)) l = mid; else r = mid;
        }
        ans = max(ans, i + 2 * l);
    }
    cout << ans;
	return 0;
}

Compilation message (stderr)

lampice.cpp: In function 'int main()':
lampice.cpp:110:25: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
  110 |             int mid = l + r >> 1;
      |                       ~~^~~
lampice.cpp:92:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   92 |   freopen(task".inp", "r",  stdin);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
lampice.cpp:93:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   93 |   freopen(task".out", "w", stdout);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 17 / 17
• Subtask 2: 25 / 25
• Subtask 3: 31 / 31
• Subtask 4: 37 / 37