Submission #406772

#	Time	Username	Problem	Language	Result	Execution time	Memory
406772		Joshc	Islands (IOI08_islands)	C++11	90 / 100	937 ms	131072 KiB

islands

#include <cstdio>
#include <vector>
#include <algorithm>
using namespace std;
 
const int MAX_N = 1000001;

#define pii pair<int, int>
#define f first
#define s second
#define ll long long

int t[MAX_N], l[MAX_N], vis[MAX_N], b;
ll m, ans = 0;
vector<int> edges[MAX_N];

void dfs2(int x, int p, ll d, vector<int> &cur) {
    cur.push_back(x);
    if (d > m) {
        m = d;
        b = x;
    }
    for (int i : edges[x]) {
        if (vis[i] && i != p) dfs2(i, x, d+l[i], cur);
    }
    if (vis[t[x]] && t[x] != p) dfs2(t[x], x, d+l[x], cur);
}

void dfs3(int x, int p, ll d) {
    m = max(m, d);
    for (int i : edges[x]) {
        if ((vis[x] || vis[i]) && i != p) dfs3(i, x, d+l[i]);
    }
    if ((vis[x] || vis[t[x]]) && t[x] != p) dfs3(t[x], x, d+l[x]);
}

void solve(int v) {
    ll best = 0, len = l[v], psa = 0, x = -1e9, y = -1e9;
    for (int i=t[v]; i!=v; i=t[i]) len += l[i];
    int i = v;
    do {
        vector<int> cur;
        m = -1;
        dfs2(i, i, 0, cur);
        best = max(best, max(psa+m+x, len+m-psa+y));
        x = max(x, m-psa);
        y = max(y, m+psa);
        psa += l[i];
        m = -1;
        dfs3(b, b, 0);
        best = max(best, m);
        i = t[i];
    } while (i != v);
    ans += best;
}

void dfs(int v, int c) {
    vis[v] = c;
    if (vis[t[v]] == c) {
        vis[v] = 0;
        for (int i=t[v]; i!=v; i=t[i]) vis[i] = 0;
        solve(v);
    }
    if (vis[t[v]] == -1) dfs(t[v], c);
}

int main() {
    int n;
    scanf("%d", &n);
    for (int i=1; i<=n; i++) {
        scanf("%d%d", &t[i], &l[i]);
        vis[i] = -1;
        edges[t[i]].push_back(i);
    }
    for (int i=1; i<=n; i++) {
        if (vis[i] == -1) dfs(i, i);
    }
    printf("%lld\n", ans);
}

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:69:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   69 |     scanf("%d", &n);
      |     ~~~~~^~~~~~~~~~
islands.cpp:71:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   71 |         scanf("%d%d", &t[i], &l[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: 10 / 10
• Subtask 9: 0 / 10