BZOJ3037 创世纪（基环树DP）

基环树DP，攻的当受的儿子，f表选，g表不选。并查集维护攻受关系。若有环则记录，DP受的后把它当祖宗，再DP攻的。

#include <cstdio>

#include <iostream>

#include <cstring>

#include <algorithm>

#include <cmath>

#define R(a,b,c) for(register int a = (b); (a) <= (c); ++(a))

#define nR(a,b,c) for(register int a = (b); (a) >= (c); --(a))

#define Fill(a,b) memset(a, b, sizeof(a))

#define Swap(a,b) ((a) ^= (b) ^= (a) ^= (b))

#define ll long long

#define u32 unsigned int

#define u64 unsigned long long

#define ON_DEBUGG

#ifdef ON_DEBUGG

#define D_e_Line printf("\n----------\n")

#define D_e(x) cout << (#x) << " : " << x << endl

#define Pause() system("pause")

#define FileOpen() freopen("in.txt", "r", stdin)

#define FileSave() freopen("out.txt", "w", stdout)

#include <ctime>

#define TIME() fprintf(stderr, "\ntime: %.3fms\n", clock() * 1000.0 / CLOCKS_PER_SEC);

#else

#define D_e_Line ;

#define D_e(x) ;

#define Pause() ;

#define FileOpen() ;

#define FileSave() ;

#define TIME() ;

//char buf[1 << 21], *p1 = buf, *p2 = buf;

//#define getchar() (p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, 1 << 21, stdin), p1 == p2) ? EOF : *p1++)

#endif

using namespace std;

struct ios{

    template<typename ATP>inline ios& operator >> (ATP &x){

        x = 0; int f = 1; char ch;

        for(ch = getchar(); ch < '0' || ch > '9'; ch = getchar()) if(ch == '-') f = -1;

        while(ch >= '0' && ch <= '9') x = x * 10 + (ch ^ '0'), ch = getchar();

        x *= f;

        return *this;

    }

}io;

template<typename ATP>inline ATP Max(ATP a, ATP b){

    return a > b ? a : b;

}

template<typename ATP>inline ATP Min(ATP a, ATP b){

    return a < b ? a : b;

}

template<typename ATP>inline ATP Abs(ATP a){

    return a < 0 ? -a : a;

}

const int N = 1000007;

int n, totCircle;

int ans, root;

int f[N], g[N], A[N], B[N];

struct Edge{

	int nxt, pre;

}e[N << 1];

int head[N], cntEdge;

inline void add(int u, int v){

	e[++cntEdge] = (Edge){ head[u], v}, head[u] = cntEdge;

}

int fa[N];

inline int Find(int x){

	return fa[x] == x ? x : fa[x] = Find(fa[x]);

}

inline void DFS(int u){

	int t = 0x7fffffff;

	g[u] = 0;

	for(register int i = head[u]; i; i = e[i].nxt){

		int v = e[i].pre;

		if(v != root) DFS(v);

		g[u] += max(f[v], g[v]);

		t = min(t, max(f[v], g[v]) - g[v]);

	}

	f[u] = g[u] + 1 - t;

}

int main(){

//FileOpen();

    io >> n;

    R(i,1,n) fa[i] = i;

    R(i,1,n){

    	int j;

        io >> j;

        int p = Find(i), q = Find(j);

        if(p != q){

        	add(j, i);

        	fa[q] = p;

		}

		else{

			A[++totCircle] = j, B[totCircle] = i;

		}

    }

    R(i,1,totCircle){

    	DFS(A[i]), root = A[i];

    	DFS(B[i]);

    	int tmp = f[B[i]];

    	f[A[i]] = g[A[i]] + 1;

    	DFS(B[i]);

    	ans += Max(tmp, g[B[i]]);

	}

    printf("%d",ans);

    return 0;

}

BZOJ3037 创世纪（基环树DP）的相关教程结束。