spoj 6779. Can you answer these queries VII(树链剖分)
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题意:给出一棵树,每个点有权值,有两种操作,一种是查询u到v路径之间最大连续子段和,另一种是修改u到v路径上的点权。
思路:树链剖分直接搞……终于把GSS系列都切掉了(泪目),之前看了看别人的树链剖分的写法,感觉自己写得实在是太挫了,所以这次按着别人的方式写了下,感觉还是挺好用的,也许是这题处理起来挺麻烦,代码还是写的非常长……查询的时候,不断维护到当前点的最大连续子段和以及到当前点的最大后缀,最后到达最近公共祖先时合并一下就行了。
代码:
#include<iostream>#include<cstdio>#include<cstring>#include<string>#include<algorithm>#include<map>#include<queue>#include<set>#include<stack>#include<cmath>#include<vector>#define inf 0x3f3f3f3f#define Inf 0x3FFFFFFFFFFFFFFFLL#define eps 1e-9#define pi acos(-1.0)using namespace std;typedef long long ll;const int maxn=100000+10;struct Edge{ int u,v,next; Edge(){}; Edge(int uu,int vv,int nx) {u=uu;v=vv;next=nx;}}edges[maxn<<1];int d[maxn],pa[maxn],fp[maxn],vson[maxn],num[maxn];int head[maxn],id[maxn],val[maxn],nEdge,N,n;void AddEdges(int u,int v){ edges[++nEdge]=Edge(u,v,head[u]); head[u]=nEdge; edges[++nEdge]=Edge(v,u,head[v]); head[v]=nEdge;}void Init(){ memset(head,0xff,sizeof(head)); memset(d,0,sizeof(d)); memset(vson,0xff,sizeof(vson)); memset(id,0xff,sizeof(id)); nEdge=-1;N=0;}int dfs(int u,int fa){ int csum=1,cmax=0,me=-1; for(int k=head[u];k!=-1;k=edges[k].next) { int v=edges[k].v; if(v==fa) continue; d[v]=d[u]+1;pa[v]=u; int cc=dfs(v,u); csum+=cc; if(cc>cmax) {cmax=cc;me=v;} } vson[u]=me; return csum;}void dfs2(int u,int fa){ if(vson[u]!=-1) { id[u]=++N; if(fa==-1||vson[fa]!=u) fp[u]=u; else fp[u]=fp[fa]; dfs2(vson[u],u); } else if(fa==-1||vson[fa]==u) id[u]=++N,fp[u]=(fa==-1)?u:fp[fa]; for(int k=head[u];k!=-1;k=edges[k].next) { int v=edges[k].v; if(v==fa||v==vson[u]) continue; fp[v]=v; dfs2(v,u); }}struct SegTree{ int sum[maxn<<2],maxs[maxn<<2]; int mpre[maxn<<2],msuff[maxn<<2],setv[maxn<<2]; void PushUp(int rt) { int ls=rt<<1,rs=rt<<1|1; sum[rt]=sum[ls]+sum[rs]; maxs[rt]=max(maxs[ls],maxs[rs]); maxs[rt]=max(maxs[rt],msuff[ls]+mpre[rs]); mpre[rt]=max(mpre[ls],sum[ls]+mpre[rs]); msuff[rt]=max(msuff[rs],sum[rs]+msuff[ls]); } void PushDown(int l,int r,int rt) { if(setv[rt]!=-inf) { int ls=rt<<1,rs=rt<<1|1,m=(l+r)>>1; setv[ls]=setv[rs]=setv[rt]; sum[ls]=(m-l+1)*setv[rt]; sum[rs]=(r-m)*setv[rt]; if(setv[rt]>0) { mpre[ls]=msuff[ls]=maxs[ls]=sum[ls]; mpre[rs]=msuff[rs]=maxs[rs]=sum[rs]; } else { mpre[ls]=msuff[ls]=maxs[ls]=setv[rt]; mpre[rs]=msuff[rs]=maxs[rs]=setv[rt]; } setv[rt]=-inf; } } void build(int l,int r,int rt) { setv[rt]=-inf; if(l==r) { sum[rt]=maxs[rt]=mpre[rt]=msuff[rt]=val[l]; return ; } int m=(l+r)>>1; build(l,m,rt<<1); build(m+1,r,rt<<1|1); PushUp(rt); } int Query(int L,int R,int l,int r,int rt,int &qsum,int &mp,int &ms) { if(l>=L&&r<=R) { qsum=sum[rt];mp=mpre[rt];ms=msuff[rt]; return maxs[rt]; } PushDown(l,r,rt); int m=(l+r)>>1; if(m>=R) return Query(L,R,l,m,rt<<1,qsum,mp,ms); else if(m<L) return Query(L,R,m+1,r,rt<<1|1,qsum,mp,ms); else { int qsum1,qsum2,mp1,mp2,ms1,ms2; int s1=Query(L,R,l,m,rt<<1,qsum1,mp1,ms1); int s2=Query(L,R,m+1,r,rt<<1|1,qsum2,mp2,ms2); s1=max(s1,s2); s1=max(s1,ms1+mp2); qsum=qsum1+qsum2; mp=max(mp1,qsum1+mp2); ms=max(ms2,qsum2+ms1); return s1; } } void Update(int L,int R,int l,int r,int rt,int v) { if(l>=L&&r<=R) { setv[rt]=v; sum[rt]=(r-l+1)*v; if(v>0) mpre[rt]=msuff[rt]=maxs[rt]=sum[rt]; else mpre[rt]=msuff[rt]=maxs[rt]=v; return ; } PushDown(l,r,rt); int m=(l+r)>>1; if(m>=L) Update(L,R,l,m,rt<<1,v); if(m<R) Update(L,R,m+1,r,rt<<1|1,v); PushUp(rt); }}segtree;int getMax(int x,int y){ int xmax=0,ymax=0,xsuf=0,ysuf=0; int qsum,mp,ms,tmp; while(fp[x]!=fp[y]) { if(d[fp[x]]<d[fp[y]]) { swap(x,y);swap(xmax,ymax); swap(xsuf,ysuf); } if(id[x]==-1) {xmax=max(xmax,num[x]);xsuf=max(xsuf,num[x]);} else { tmp=segtree.Query(id[fp[x]],id[x],1,N,1,qsum,mp,ms); xmax=max(xmax,tmp); xmax=max(xmax,xsuf+ms); xsuf=max(mp,qsum+xsuf); } x=pa[fp[x]]; } if(d[x]<d[y]) { swap(x,y);swap(xmax,ymax); swap(xsuf,ysuf); } if(id[x]==-1) {xmax=max(xmax,num[x]);xsuf=max(xsuf,num[x]);} else { tmp=segtree.Query(id[y],id[x],1,N,1,qsum,mp,ms); xmax=max(xmax,tmp); xmax=max(xmax,xsuf+ms); xsuf=max(mp,qsum+xsuf); } xmax=max(xmax,ymax); xmax=max(xmax,xsuf+ysuf); return max(xmax,0);}void changes(int x,int y,int v){ while(fp[x]!=fp[y]) { if(d[fp[x]]<d[fp[y]]) swap(x,y); if(id[x]==-1) num[x]=v; else segtree.Update(id[fp[x]],id[x],1,N,1,v); x=pa[fp[x]]; } if(d[x]<d[y]) swap(x,y); if(id[x]==-1) num[x]=v; else segtree.Update(id[y],id[x],1,N,1,v);}int main(){ //freopen("in.txt","r",stdin); //freopen("out.txt","w",stdout); while(~scanf("%d",&n)) { Init(); for(int i=1;i<=n;++i) scanf("%d",&num[i]); int u,v; for(int i=1;i<n;++i) { scanf("%d%d",&u,&v); AddEdges(u,v); } dfs(1,-1); dfs2(1,-1); for(int i=1;i<=n;++i) if(id[i]!=-1) val[id[i]]=num[i]; if(N) segtree.build(1,N,1); int q,type,a,b,c; scanf("%d",&q); while(q--) { scanf("%d",&type); if(type==1) { scanf("%d%d",&a,&b); printf("%d\n",getMax(a,b)); } else { scanf("%d%d%d",&a,&b,&c); changes(a,b,c); } } } return 0;}
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