Submission #921163

#	Time	Username	Problem	Language	Result	Execution time	Memory
921163		Beerus13	Lampice (COCI19_lampice)	C++14	110 / 110	1823 ms	14424 KiB

lampice

#include<bits/stdc++.h>
using namespace std;
#define ll long long 
const int N = 5e4 + 5;
const int mod = 1e9 + 7;
const int base = 31;
 
int n, sz[N], Pow[N], dep[N], up[N], down[N];
string s;
vector<int> g[N];
bool del[N];
unordered_set<int> sett[N];
int mx, centroid, len;
 
int dfs_size(int u, int p = 0) {
    sz[u] = 1;
    for(int v : g[u]) if(v != p && !del[v]) {
        sz[u] += dfs_size(v, u);
    }
    return sz[u];
}
 
int find_centroid(int u, int p, int num) {
    for(int v : g[u]) if(v != p && !del[v] && sz[v] > num / 2) return find_centroid(v, u, num);
    return u;
}
 
void dfs_centroid(int u, int p, bool upd, bool &found) {
    dep[u] = dep[p] + 1;
    up[u] = (1ll * up[p] * base + s[u] - 'a' + 1) % mod;
    down[u] = (down[p] + 1ll * Pow[dep[u] - 1] * (s[u] - 'a' + 1)) % mod;
    int val = (1ll * down[u] * Pow[len - dep[u]] - up[u]) % mod; if(val < 0) val += mod;
    if(upd) sett[dep[u]].insert(val);
    else {
        if(dep[u] + 1 == len && up[u] == (1ll * down[u] * base + s[centroid] - 'a' + 1) % mod) {
            found = 1;
            return;
        }
        if(dep[u] < len && sett[len - dep[u] - 1].find(val) != sett[len - dep[u] - 1].end()) {
            found = 1;
            return;
        }
    }
    if(dep[u] < len) {
        for(int v : g[u]) if(v != p && !del[v])  {
            dfs_centroid(v, u, upd, found);
            mx = max(mx, dep[u] + 1);
            if(found) return;
        }
    }
}
 
void calc(int u, bool &found) {
    centroid = find_centroid(u, 0, dfs_size(u));
    del[centroid] = 1;
    mx = 1;
    up[centroid] = s[centroid] - 'a' + 1;
    down[centroid] = 0;
    dep[centroid] = 0;
    for(int v : g[centroid]) if(!del[v]) {
        dfs_centroid(v, centroid, 0, found);
        if(found) return;
        dfs_centroid(v, centroid, 1, found);
    }
    for(int i = 0; i <= mx; ++i) sett[i].clear();
    for(int v : g[centroid]) if(!del[v]) {
        calc(v, found);
        if(found) return;
    }
 
}
 
bool check(int x) {
    for(int i = 0; i <= n; ++i) sett[i].clear();
    memset(del, 0, sizeof(del));
    bool found = 0; len = x;
    calc(1, found);
    return found;
}
 
void solve() {
    cin >> n >> s; s = ' ' + s;
    Pow[0] = 1; for(int i = 1; i <= n; ++i) Pow[i] = (1ll * Pow[i - 1] * base) % mod;
    for(int i = 1, u, v; i < n; ++i) {
        cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    int ans = 1;
    for(int i = 0; i < 2; ++i) {
        int l = 0, r = n / 2 + 1;
        while(r - l > 1) {
            int m = l + r >> 1;
            if(check(i + 2 * m)) l = m;
            else r = m;
        }
        ans = max(ans, i + 2 * l);
    }
    cout << ans << '\n';
}
 
signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    int test = 1;
    // cin >> test;
    while(test--) solve();
    return 0;
}
 
// https://oj.uz/problem/view/COCI19_lampice

Compilation message (stderr)

lampice.cpp: In function 'void solve()':
lampice.cpp:93:23: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   93 |             int m = l + r >> 1;
      |                     ~~^~~

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