【DP】 BZOJ 1487: [HNOI2009]无归岛

#include <iostream>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <bitset>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <climits>
#include <cstdlib>
#include <cmath>
#include <time.h>
#define maxn 100005
#define maxm 500005
#define eps 1e-7
#define mod 1000000007
#define INF 0x3f3f3f3f
#define PI (acos(-1.0))
#define lowbit(x) (x&(-x))
#define mp make_pair
#define ls o<<1
#define rs o<<1 | 1
#define lson o<<1, L, mid
#define rson o<<1 | 1, mid+1, R
#define pii pair<int, int>
#pragma comment(linker, "/STACK:16777216")
typedef long long LL;
typedef unsigned long long ULL;
//typedef int LL;
using namespace std;
LL qpow(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base;base=base*base;b/=2;}return res;}
LL powmod(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base%mod;base=base*base%mod;b/=2;}return res;}
// head

struct Edge
{
int v;
Edge *next;
}E[maxm], *H[maxn], *edges;

int dfn[maxn];
int low[maxn];
int val[maxn];
int f[2][maxn];
int fa[maxn];
int a[maxn];
int n, m, dfs_clock;

void addedges(int u, int v)
{
edges->v = v;
edges->next = H[u];
H[u] = edges++;
}

void init()
{
dfs_clock = 0;
edges = E;
memset(H, 0, sizeof H);
memset(f, 0, sizeof f);
memset(dfn, 0, sizeof dfn);
}

void dp(int cnt)
{
//	for(int i = 0; i < cnt; i++) printf("PPP %d %d\n", f[0][a[i]], f[1][a[i]]);
int res1 = 0, res2 = 0, t1, t2;
for(int i = 1; i < cnt; i++) {
t1 = max(res1, res2) + f[0][a[i]];
t2 = res1 + f[1][a[i]];
res1 = t1, res2 = t2;
}
f[0][a[0]] += max(res1, res2);

res1 = res2 = 0;
for(int i = 2; i < cnt - 1; i++) {
t1 = max(res1, res2) + f[0][a[i]];
t2 = res1 + f[1][a[i]];
res1 = t1, res2 = t2;
}

f[1][a[0]] += max(res1, res2) + f[0][a[1]] + f[0][a[cnt-1]];
}
void dfs(int u)
{
dfn[u] = low[u] = ++dfs_clock;
for(Edge *e = H[u]; e; e = e->next) if(e->v != fa[u]) {
int v = e->v;
if(!dfn[v]) {
fa[v] = u;
dfs(v);
low[u] = min(low[u], low[v]);
}
else low[u] = min(low[u], dfn[v]);
}
f[0][u] = 0, f[1][u] = val[u];

for(Edge *e = H[u]; e; e = e->next) if(e->v != fa[u]) {
int v = e->v;
if(u == fa[v] && dfn[u] < low[v]) {
f[0][u] += max(f[0][v], f[1][v]);
f[1][u] += f[0][v];
}
}

for(Edge *e = H[u]; e; e = e->next) if(e->v != fa[u]) {
int v = e->v;
if(u != fa[v] && dfn[u] == low[v]) {
int cnt = 0, vn = v;
a[cnt++] = u;
do {
a[cnt++] = vn;
vn = fa[vn];
}while(vn != u);
dp(cnt);
}
}
}

void work()
{
int u, v;
while(m--) {
scanf("%d%d", &u, &v);
addedges(u, v);
addedges(v, u);
}

for(int i = 1; i <= n; i++) scanf("%d", &val[i]), val[i] = max(0, val[i]);

fa[1] = 0;
dfs(1);
int ans = max(f[0][1], f[1][1]);
printf("%d\n", ans);
}

int main()
{
while(scanf("%d%d", &n, &m) != EOF) {
init();
work();
}

return 0;
}