洛谷 2921 在牧场万圣节

Tarjan + DAG上跑PD

#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cctype>
#include <cstdio>

using namespace std;

inline void read(int &x)
{
    int k = 1; x = 0;
    char ch = getchar();
    while (!isdigit(ch)) 
        if (ch == '-') ch = getchar(), k = -1;
        else ch = getchar();
    while (isdigit(ch))
        x = (x << 1) + (x << 3) + (ch ^ 48),
        ch = getchar();
    x *= k;
}

const int N = 101010; 
int n, cnt = 0, x, top, color = 0, tag = 0, cur, cnt2 = 0;
int f[N], v[N], dfn[N], low[N], stk[N], col[N], F[N], in[N], sum[N], ans[N];

struct Edge
{
    int u, v, nxt;
}e[N << 2], E[N << 2];

inline void Addedge(int a, int b)
{
    ++cnt;
    e[cnt].u = a;
    e[cnt].v = b;
    e[cnt].nxt = f[a];
    f[a] = cnt;
}

inline void addedge(int a, int b)
{
    ++cnt2;
    E[cnt2].u = a;
    E[cnt2].v = b;
    E[cnt2].nxt = F[a];
    F[a] = cnt2;
}

void Tarjan(int u)
{
    dfn[u] = low[u] = ++tag;
    stk[++top] = u; v[u] = 1;
    for (int i = f[u]; i != -1; i = e[i].nxt)
        if (!dfn[e[i].v])
            Tarjan(e[i].v), low[u] = min(low[u], low[e[i].v]);
        else if (v[e[i].v])
            low[u] = min(low[u], low[e[i].v]);
    if (dfn[u] == low[u])
    {
        ++color;
        do
        {
            cur = stk[top--];
            col[cur] = color;
            ++sum[color];
            v[cur] = 0;
        }while (cur != u);
    }
}

void DFS(int u)
{
    for (int i = F[u]; i != -1; i = E[i].nxt)
        ans[E[i].v] += ans[u], DFS(E[i].v);
}

int main()
{
    read(n);
    memset(f, -1, sizeof(f));
    memset(F, -1, sizeof(F));
    for (int i = 1; i <= n; ++i) { read(x); if (i != x) Addedge(i, x); }
    for (int i = 1; i <= n; ++i) if (!dfn[i]) Tarjan(i);
    for (int i = 1; i <= cnt; ++i)
        if (col[e[i].v] != col[e[i].u])
            addedge(col[e[i].v], col[e[i].u]), ++in[col[e[i].u]];
    for (int i = 1; i <= color; ++i) ans[i] = sum[i];
    for (int i = 1; i <= color; ++i) if (!in[i]) DFS(i);
    for (int i = 1; i <= n; ++i) printf("%d
", ans[col[i]]);
    return 0;
}