Submission #390231

#	Time	Username	Problem	Language	Result	Execution time	Memory
390231		parsabahrami	Islands (IOI08_islands)	C++17	80 / 100	1886 ms	131076 KiB

islands

/* There's someone in my head but it's not me */ 
#include <bits/stdc++.h>
 
using namespace std;

typedef long long int ll;
typedef pair<int, int> pii;
 
#define SZ(x)                       (int) x.size()
#define F                           first
#define S                           second

const int N = 1e6 + 1;
int n, rt[N], P[N], C[N], M[N], out[N], w[N], R; ll A[N], ret[N], H[N], S[N];
vector<int> adj[N], vec; vector<vector<int>> comps;

int Find(int v) {
    return !rt[v] ? v : rt[v] = Find(rt[v]);
}

int Union(int v, int u) {
    u = Find(u), v = Find(v);
    if (u == v) return 1;
    rt[u] = v; 
    return 0;
}

void preDFS(int v, int tr, int p = -1) {
    vec.push_back(v);
    for (int id : adj[v]) {
        int u = out[id] ^ id ^ v;
        if ((!C[u] || u == tr) && u != p) 
            H[u] = H[v] + w[id], preDFS(u, tr, v);
    }
}

void cycDFS(int v, int tr, int p = -1) {
    P[v] = p; vec.push_back(v);
    for (int id : adj[v]) {
        if (id != tr) {
            int u = out[id] ^ id ^ v;
            if (u != p) cycDFS(u, tr, v);
        }
    }
}


ll CYC(int v, int p = -1) {
    ll ans = -1e18;
    for (int id : adj[v]) {
        int u = out[id] ^ id ^ v;
        if (C[u] && u != p && u != R) {
            H[u] = H[v] + w[id], ans = CYC(u, v);
            break;
        }
    }
    ret[Find(v)] =  max(ret[Find(v)], ans + A[v] - H[v]);
    return max(ans, A[v] + H[v]);
}

ll CYC2(int v, int p = -1) {
    ll ans = -1e18;
    for (int id : adj[v]) {
        int u = out[id] ^ id ^ v;
        if (C[u] && u != p && u != R) {
            ans = CYC2(u, v);
            break;
        }
    }
    ret[Find(v)] = max(ret[Find(v)], ans + A[v] + H[v]);
    return max(ans, S[Find(v)] - H[v] + A[v]);
}

int main() {
    scanf("%d", &n);
    vector<int> bads;
    for (int i = 1; i <= n; i++) {
        scanf("%d%d", &out[i], &w[i]);
        adj[i].push_back(i);
        adj[out[i]].push_back(i);
        if (Union(i, out[i])) 
            bads.push_back(i);
    } 
    for (int id : bads) {
        vec = {};
        cycDFS(out[id], id); 
        comps.push_back(vec);
        int v = id; 
        while (~v) 
            C[v] = 1, v = P[v];
    } 
    for (int i = 1; i <= n; i++) {
        if (!C[i]) continue;
        vec = {}, preDFS(i, i);
        for (int id : adj[i]) {
            int u = out[id] ^ id ^ i;
            if (C[u]) S[Find(i)] += w[id];
        }
        int b = -1;
        for (int v : vec) 
            if (!~b || H[b] < H[v]) b = v;
        A[i] = H[b]; vec = {};
        H[b] = 0, preDFS(b, i);
        b = -1;
        for (int v : vec) 
            if (!~b || H[b] < H[v]) b = v;
        ret[Find(i)] = max(ret[Find(i)], H[b]);
    }
    ll res = 0;
    for (auto &c : comps) {
        S[Find(c.back())] >>= 1;
        for (int &v : c) 
            if (C[v]) R = v; 
        H[R] = 0;
        CYC(R), CYC2(R);
        res += ret[Find(c.back())];
    }
    printf("%lld\n", res);
    return 0;
}

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:75:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   75 |     scanf("%d", &n);
      |     ~~~~~^~~~~~~~~~
islands.cpp:78:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   78 |         scanf("%d%d", &out[i], &w[i]);
      |         ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 33 / 33
• Subtask 2: 3 / 3
• Subtask 3: 4 / 4
• Subtask 4: 10 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 10 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10