SPOJ GSS2 Can you answer these queries II (线段树&离线) - xgtao -
Can you answer these queries II
这是一道线段树的题目,维护历史版本,给出N(<=100000)个数字(-100000<=x<=100000),要求求出在[l,r]区间里面的连续序列的最大值,并且重复的数字可以加入序列但是值不能再计算。
本题明显使用线段树,它只存在询问而没有修改操作,离线相对于在线更好维护。
定义s[i] = ai + ai+1 + ai+2 + ... an,以ai开头的数列的和,那么每次加入更新ai 那么s1,s2,...si都会相应的加一个ai,s[1~i]中出现过a[i]是不能重复加值的,那么为了避免重复加值,用pre[a[i]]表示a[i]上一次出现的位置,那么也就是s[pre[ai]+1]~s[i]这一个区间加上a[i],每一次更新a[i]都要记录历史版本的最大值和懒惰标记的最大值。
#include <cstdio> #include <iostream> #include <cstring> #include <algorithm> using namespace std; const int N = 100010; const int M = 100010; const int C = 100001; long long res[N]; int a[N],pre[N<<1],n,m; struct Que{ int l,r,ID; bool operator < (const Que &rhs)const{return r < rhs.r;} }question[M]; struct Tree{long long s,ms,d,md;}tree[N<<2]; #define lson k<<1,l,mid #define rson k<<1|1,mid+1,r void processup(int k){ tree[k].s = max(tree[k<<1].s,tree[k<<1|1].s); tree[k].ms = max(tree[k<<1].ms,tree[k<<1|1].ms); } void processdown(int k){ if(!tree[k].d && !tree[k].md)return; tree[k<<1].ms = max(tree[k<<1].ms,tree[k<<1].s+tree[k].md); tree[k<<1].md = max(tree[k<<1].md,tree[k<<1].d+tree[k].md); tree[k<<1].s += tree[k].d,tree[k<<1].d += tree[k].d; tree[k<<1|1].ms = max(tree[k<<1|1].ms,tree[k<<1|1].s+tree[k].md); tree[k<<1|1].md = max(tree[k<<1|1].md,tree[k<<1|1].d+tree[k].md); tree[k<<1|1].s += tree[k].d,tree[k<<1|1].d += tree[k].d; tree[k].d = tree[k].md = 0; } long long query(int k,int l,int r,int xl,int xr){ if(l == xl && r == xr)return tree[k].ms; processdown(k); int mid = (l+r)>>1; if(xr <= mid)return query(lson,xl,xr); else if(xl > mid)return query(rson,xl,xr); else return max(query(lson,xl,mid),query(rson,mid+1,xr)); processup(k); } void update(int k,int l,int r,int xl,int xr,long long x){ if(l == xl && r == xr){ tree[k].s += x; tree[k].d += x; tree[k].ms = max(tree[k].ms,tree[k].s); tree[k].md = max(tree[k].md,tree[k].d); return; } processdown(k); int mid = (l+r)>>1; if(xr <= mid)update(lson,xl,xr,x); else if(xl > mid)update(rson,xl,xr,x); else update(lson,xl,mid,x),update(rson,mid+1,xr,x); processup(k); } #define clr(a,b) memset(a,b,sizeof(a)) int main(){ while(scanf("%d",&n) == 1){ clr(tree,0),clr(pre,0); for(int i = 1;i <= n;++i)scanf("%d",&a[i]); scanf("%d",&m); for(int i = 1;i <= m;++i){ scanf("%d%d",&question[i].l,&question[i].r); question[i].ID = i; } sort(question+1,question+m+1); int ID = 1; for(int i = 1;i <= n;++i){ update(1,1,n,pre[a[i]+C]+1,i,a[i]); pre[a[i]+C] = i; while(ID <= m && question[ID].r == i){ res[question[ID].ID] = query(1,1,n,question[ID].l,question[ID].r); ID++; } } for(int i = 1;i <= m;++i)printf("%lld\n",res[i]); } return 0; }