考虑贪心，每次选价值最大的链。选完之后对于链上点dfs序暴力修改子树。因为每个点最多被选一次，复杂度非常正确。
#include<iostream> #include<cstdio> #include<cmath> #include<cstdlib> #include<cstring> #include<algorithm> using namespace std; int read() { int x=0,f=1;char c=getchar(); while (c<'0'||c>'9') {if (c=='-') f=-1;c=getchar();} while (c>='0'&&c<='9') x=(x<<1)+(x<<3)+(c^48),c=getchar(); return x*f; } #define N 200010 #define ll long long #define inf 1000000000000000 int n,m,a[N],p[N],fa[N],id[N],dfn[N],size[N],cnt=0,t=0; bool isleaf[N],flag[N]; int L[N<<2],R[N<<2]; ll deep[N],tree[N<<2],lazy[N<<2],ans; struct data{int to,nxt; }edge[N]; void addedge(int x,int y){t++;edge[t].to=y,edge[t].nxt=p[x],p[x]=t;} void dfs(int k) { size[k]=1;deep[k]=deep[fa[k]]+a[k]; id[k]=++cnt;dfn[cnt]=k; for (int i=p[k];i;i=edge[i].nxt) if (edge[i].to!=fa[k]) dfs(edge[i].to),size[k]+=size[edge[i].to]; } void up(int k){tree[k]=max(tree[k<<1],tree[k<<1|1]);} void down(int k) { tree[k<<1]+=lazy[k],tree[k<<1|1]+=lazy[k]; lazy[k<<1]+=lazy[k],lazy[k<<1|1]+=lazy[k]; lazy[k]=0; } void build(int k,int l,int r) { L[k]=l,R[k]=r; if (l==r) {tree[k]=isleaf[dfn[l]]?deep[dfn[l]]:-inf;return;} int mid=l+r>>1; build(k<<1,l,mid); build(k<<1|1,mid+1,r); up(k); } int query(int k) { if (L[k]==R[k]) return L[k]; if (lazy[k]) down(k); if (tree[k<<1]>tree[k<<1|1]) return query(k<<1); else return query(k<<1|1); } void add(int k,int l,int r,int x) { if (L[k]==l&&R[k]==r) {tree[k]+=x,lazy[k]+=x;return;} if (lazy[k]) down(k); int mid=L[k]+R[k]>>1; if (r<=mid) add(k<<1,l,r,x); else if (l>mid) add(k<<1|1,l,r,x); else add(k<<1,l,mid,x),add(k<<1|1,mid+1,r,x); up(k); } int main() { #ifndef ONLINE_JUDGE freopen("bzoj3252.in","r",stdin); freopen("bzoj3252.out","w",stdout); const char LL[]="%I64d "; #else const char LL[]="%lld "; #endif n=read(),m=read(); for (int i=1;i<=n;i++) a[i]=read(),isleaf[i]=1; for (int i=1;i<n;i++) { int x=read(),y=read(); addedge(x,y);fa[y]=x;isleaf[x]=0; } dfs(1); build(1,1,n); flag[0]=1; while (m--) { if (tree[1]<=0) break; ans+=tree[1]; int x=dfn[query(1)]; while (!flag[x]) { flag[x]=1; add(1,id[x],id[x]+size[x]-1,-a[x]); x=fa[x]; } } cout<<ans; return 0; }