代码模板-线段树（区间修改，区间查询和和最值）

题目链接：1270. 数列区间最大值 - AcWing题库

代码：

// #pragma GCC optimize(1)
// #pragma GCC optimize(2)
// #pragma GCC optimize(3,"Ofast","inline")

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define inf 1e10
#define N 100010
#define ls u<<1
#define rs ls|1

struct Node{
    ll l,r;
    ll sum,add,mx;
}tr[N<<2];

ll n,m;
ll a[N];

void pushup(ll u){
    tr[u].sum=tr[ls].sum+tr[rs].sum;
    tr[u].mx=max(tr[ls].mx,tr[rs].mx);
}

void pushdown(ll u){
    if(tr[u].add){
        tr[ls].add+=tr[u].add;
        tr[rs].add+=tr[u].add;
        tr[ls].sum+=(tr[ls].r-tr[ls].l+1)*tr[u].add;
        tr[rs].sum+=(tr[rs].r-tr[rs].l+1)*tr[u].add;
        tr[ls].mx+=tr[u].add;
        tr[rs].mx+=tr[u].add;
        tr[u].add=0;
    }
}

void build(ll u,ll l,ll r){
    if(l==r)tr[u]={l,r,a[l],0,a[l]};
    else{
        ll mid=l+r>>1;
        tr[u]={l,r};
        build(ls,l,mid),build(rs,mid+1,r);
        pushup(u);
    }
}

ll querySum(ll u,ll l,ll r){
    if(l<=tr[u].l&&tr[u].r<=r)return tr[u].sum;
    else{
        pushdown(u);
        ll mid=tr[u].l+tr[u].r>>1;
        ll sum=0;
        if(l<=mid)sum+=querySum(ls,l,r);
        if(r>mid)sum+=querySum(rs,l,r);
        return sum;
    }
}

ll queryMx(ll u,ll l,ll r){
    if(l<=tr[u].l&&tr[u].r<=r)return tr[u].mx;
    else{
        pushdown(u);
        ll mid=tr[u].l+tr[u].r>>1;
        ll mx=-inf;
        if(l<=mid)mx=max(mx,queryMx(ls,l,r));
        if(r>mid)mx=max(mx,queryMx(rs,l,r));
        return mx;
    }
}

ll modify(ll u,ll l,ll r,ll w){
    // cout<<u<<" "<<l<<" "<<r<<" "<<w<<endl;
    if(l<=tr[u].l&&tr[u].r<=r){
        tr[u].add+=w;
        tr[u].sum+=(tr[u].r-tr[u].l+1)*w;
        tr[u].mx+=w;
    }else{
        pushdown(u);
        ll mid=tr[u].l+tr[u].r>>1;
        if(l<=mid)modify(ls,l,r,w);
        if(r>mid)modify(rs,l,r,w);
        pushup(u);
    }
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    cin>>n>>m;
    
    build(1,1,n);
    
    for(int i=1;i<=n;i++)cin>>a[i];
    
    for(int i=1;i<=n;i++)modify(1,i,i,a[i]);
    
    while(m--){
        int l,r;
        cin>>l>>r;
        cout<<queryMx(1,l,r)<<'\n';
    }
    
    
    return 0;
}