HDU 1754 I Hate It
题解：线段树单点更新区间求极值。
#include <cstdio>
#include <algorithm>
using namespace std;
int a,b,q[200005],t[1200000];
void build(int l,int r,int x){
int mid=(l+r)>>1;
if(l==r){t[x]=q[mid];return;}
build(l,mid,x<<1);
build(mid+1,r,x<<1|1);
t[x]=max(t[x<<1],t[x<<1|1]);
}
int query(int l,int r,int x){
if(a<=l&&b>=r)return t[x];
else{
int mid=(l+r)>>1;
if(b<=mid)return query(l,mid,x<<1);
else if(a>mid)return query(mid+1,r,x<<1|1);
else return max(query(l,mid,x<<1),query(mid+1,r,x<<1|1));
}
}
void modify(int l,int r,int x){
if(l==r){t[x]=b;return;}
int mid=(l+r)>>1;
if(a<=mid)modify(l,mid,x<<1),t[x]=max(t[x<<1],t[x<<1|1]);
else{modify(mid+1,r,x<<1|1),t[x]=max(t[x<<1],t[x<<1|1]);}
}
int main(){
int m,n; char op[3];
while(~scanf("%d%d",&n,&m)){
for(int i=1;i<=n;i++)scanf("%d",&q[i]);
build(1,n,1);
while(m--){
scanf("%s%d%d",&op,&a,&b);
if(op[0]=='Q')printf("%d\n",query(1,n,1));
else modify(1,n,1);
}
}
return 0;
}
当然分块处理也可以过
#include <cstdio>
#include <algorithm>
using namespace std;
char op[6];
int st[200005],en[200005],p[2000],i,size,block,a[200005],m,n,pos[200005],x,y;
int main(){
while(~scanf("%d%d",&n,&m)){
size=0;
while(size*size<n)size++;pos[n]=(n-1)/size+1;
for(int i=0;i<=size;i++)p[i]=-2147400000;
for(block=pos[n],i=1;i<=block;i++)en[i-1]=(st[i]=size*(i-1)+1)-1;en[block]=n;
for(i=1;i<=n;i++)scanf("%d",&a[i]),pos[i]=(i-1)/size+1,p[pos[i]]=max(p[pos[i]],a[i]);
while(m--){
scanf("%s%d%d",op,&x,&y);
if(op[0]=='U'){
int k=pos[x];
p[k]=y; a[x]=y;
for(int i=st[k];i<=en[k];i++)if(a[i]>p[k])p[k]=a[i];
}
if(op[0]=='Q'){
int ans=-2147400000;
if(pos[x]==pos[y]){
for(int i=x;i<=y;i++)ans=max(ans,a[i]);
}else{
for(int i=x;i<=en[pos[x]];i++)ans=max(ans,a[i]);
for(int i=st[pos[y]];i<=y;i++)ans=max(ans,a[i]);
for(int i=pos[x]+1;i<pos[y];i++)ans=max(ans,p[i]);
}
printf("%d\n",ans);
}
}
}return 0;
}