线段树最大子段模板
struct node{
int l,r;
int sum,ms;//maxsum
int ml,mr;//maxl,maxr
}tree[N*4];
void PushUp(int i)
{
tree[i].sum=tree[i<<1].sum+tree[i<<1|1].sum;
tree[i].ml=max(tree[i<<1].sum+tree[i<<1|1].ml,tree[i<<1].ml);
tree[i].mr=max(tree[i<<1|1].sum+tree[i<<1].mr,tree[i<<1|1].mr);
tree[i].ms=max(max(tree[i<<1].ms,tree[i<<1|1].ms),tree[i<<1].mr+tree[i<<1|1].ml);
}
void build(int i,int l,int r)
{
tree[i].l=l,tree[i].r=r;
if(l==r)
{
tree[i].sum=tree[i].ml=tree[i].mr=tree[i].ms=a[l];
return ;
}
int mid=(l+r)>>1;
build(i<<1,l,mid);
build(i<<1|1,mid+1,r);
PushUp(i);
}
void update(int i,int pos,int val)
{
if(tree[i].l==tree[i].r)
{
tree[i].ms=tree[i].ml=tree[i].mr=tree[i].sum=val;
return ;
}
int mid=(tree[i].l+tree[i].r)>>1;
if(pos<=mid)
update(i<<1,pos,val);
else update(i<<1|1,pos,val);
PushUp(i);
}
node query(int i,int l,int r)
{
if(l<=tree[i].l&&tree[i].r<=r)
return tree[i];
int mid=(tree[i].l+tree[i].r)>>1;
if(r<=mid) return query(i<<1,l,r);
else if(l>mid) return query(i<<1|1,l,r);
else
{
node x=query(i<<1,l,r),y=query(i<<1|1,l,r),res;
//合并答案
res.sum=x.sum+y.sum;
res.ml=max(x.sum+y.ml,x.ml);
res.mr=max(y.sum+x.mr,y.mr);
res.ms=max(max(x.ms,y.ms),x.mr+y.ml);
return res;
}
}
参考
