提出 #27418439

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ソースコード 拡げる

// {{{
#include <bits/stdc++.h>
using namespace std;
using LL = long long;
using vi = vector<int>;
using pii = pair<int, int>;
#define sz(x) (int)((x).size())
#define all(x) (x).begin(), (x).end()
#define clr(a, b) memset(a, b, sizeof(a))
#define rep(i, a, b) for (int i = (a); i < (b); ++i)
#define debug(x...)
#define debug_arr(x...)
#ifdef LOCAL
#include "prettyprint.hpp"
#endif
// }}}

const int N = 2e5 + 10;
int head[N], e;
struct E
{
    int v, next;
} edge[N << 1];

void addedge(int u, int v)
{
    edge[e].v = v, edge[e].next = head[u];
    head[u] = e++;
}

int vis[N];
void dfs(int u, int f)
{
    if (vis[u]) return;
    vis[u] = 1;
    for (int i = head[u]; ~i; i = edge[i].next)
    {
        int v = edge[i].v;
        if (v == f) continue;

        dfs(v, u);
    }
}

int n, x;

int main()
{
#ifdef LOCAL
    freopen("in", "r", stdin);
    // freopen("out", "w", stdout);
#endif

    ios::sync_with_stdio(false);
    cin.tie(0);

    while (cin >> n >> x)
    {
        clr(head, -1), e = 0;
        for (int i = 1; i <= n; i++)
        {
            int u = i;
            int v;
            cin >> v;
            addedge(u, v);
        }

        clr(vis, false);
        dfs(x, -1);
        int ans = 0;
        for (int i = 1; i <= n; i++) ans += vis[i];
        cout << ans << '\n';
    }

    return 0;
}

提出情報

ジャッジ結果