hdu 1754 线段树单点更新求最值

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
#include<cstdlib>
#include<queue>
#define fo(i,a,b) for(int i=a;i<=b;i++)
#define fod(i,a,b) for(int i=a;i>=b;i--)
using namespace std;
#define lc (x<<1)
#define rc (x<<1|1)
#define mid ((l+r)>>1)
const int MAXN=2e5+10;
int vi[MAXN],maxs[MAXN<<2];

void build(int x,int l,int r){
if(l==r){
maxs[x]=vi[l];
return ;
}
build(lc,l,mid);
build(rc,mid+1,r);
maxs[x]=max(maxs[rc],maxs[lc]);
}

void updata(int x,int l,int r,int pos,int val){
if(l==r){
maxs[x]=val;
return ;
}
if(pos<=mid) updata(lc,l,mid,pos,val);
else updata(rc,mid+1,r,pos,val);
maxs[x]=max(maxs[lc],maxs[rc]);
}

void query(int x,int ql,int qr,int l,int r,int &ans){
if(ql<=l&&qr>=r){
ans=max(ans,maxs[x]);
return ;
}
if(ql<=mid) query(lc,ql,qr,l,mid,ans);
if(qr>mid) query(rc,ql,qr,mid+1,r,ans);
}

int n,m;

int main(){
while(scanf("%d%d",&n,&m)!=EOF){
fo(i,1,n) scanf("%d",&vi[i]);
build(1,1,n);
char c;
int a,b;
fo(i,1,m){
cin>>c;
scanf("%d%d",&a,&b);
if(c=='Q'){
int ans=0;
query(1,a,b,1,n,ans);
printf("%d\n",ans);
}
if(c=='U'){
updata(1,1,n,a,b);
}
}
}
return 0;
}