SPOJ 1043 Can you answer these queries I（GSS1 线段树）

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转载请注明出处，谢谢http://blog.csdn.net/acm_cxlove/article/details/7854526 by---cxlove

题目：查询区间最大子段和

http://www.spoj.pl/problems/GSS1/

简单线段树，可是写了好久~~~跪

维护3个值，区间的最大子段和，左端连续的最大子段和，右端连续的最大子段和

查询有点麻烦~~~查询左区间的最大值，查询右区间的最大值，然后查询两个区间的交接处。

一直不知道怎么处理，就查询了左区间的右端最大加上右区间的最端最大，效率很低

#include<iostream>#include<cstdio>#include<map>#include<cstring>#include<cmath>#include<vector>#include<queue>#include<algorithm>#include<set>#define inf (1ull<<63)-1#define N 50005#define maxn 100005#define Min(a,b) ((a)<(b)?(a):(b))#define Max(a,b) ((a)>(b)?(a):(b))#define pb(a) push_back(a)#define mem(a,b) memset(a,b,sizeof(a))#define eps 1e-9#define zero(a) fabs(a)<eps#define LL long long#define ULL unsigned long long#define lson (step<<1)#define rson (step<<1|1)#define MOD 1000000007#define mp(a,b) make_pair(a,b)using namespace std;int n,a[N],q,sum[N]={0};struct Node{int left,right,lx,rx,mx;int all(){return sum[right]-sum[left-1];}}L[N*4];void Push_Up(int step){L[step].lx=max(L[lson].lx,L[lson].all()+L[rson].lx);L[step].rx=max(L[rson].rx,L[rson].all()+L[lson].rx);L[step].mx=max(max(L[lson].mx,L[rson].mx),L[lson].rx+L[rson].lx);}void Bulid(int step,int l,int r){L[step].left=l;L[step].right=r;if(l==r){L[step].lx=L[step].rx=L[step].mx=a[l];return ;}int m=(l+r)/2;Bulid(lson,l,m);Bulid(rson,m+1,r);Push_Up(step);}int Q_L(int step,int l,int r){if(L[step].left==l&&L[step].right==r)return L[step].lx;int m=(L[step].left+L[step].right)/2;if(r<=m) return Q_L(lson,l,r);else if(l>m) return Q_L(rson,l,r);else return max(Q_L(lson,l,m),max(sum[m]-sum[l-1],sum[m]-sum[l-1]+Q_L(rson,m+1,r)));}int Q_R(int step,int l,int r){if(L[step].left==l&&L[step].right==r)return L[step].rx;int m=(L[step].left+L[step].right)/2;if(r<=m) return Q_R(lson,l,r);else if(l>m) return Q_R(rson,l,r);else return max(Q_R(rson,m+1,r),max(sum[r]-sum[m],sum[r]-sum[m]+Q_R(lson,l,m)));}int Query(int step,int l,int r){if(L[step].left==l&&L[step].right==r)return L[step].mx;int m=(L[step].left+L[step].right)/2;if(r<=m) return Query(lson,l,r);else if(l>m) return Query(rson,l,r);else return max(max(Query(lson,l,m),Query(rson,m+1,r)),Q_R(lson,l,m)+Q_L(rson,m+1,r));}int main(){while(scanf("%d",&n)!=EOF){for(int i=1;i<=n;i++) {scanf("%d",&a[i]);sum[i]=sum[i-1]+a[i];}Bulid(1,1,n);scanf("%d",&q);while(q--){int l,r;scanf("%d%d",&l,&r);printf("%d\n",Query(1,l,r));}}return 0;}