学步园

对我这种弱菜来说挺难的，算是抄的代码吧

#include <set>
#include <map>
#include <ctime>
#include <queue>
#include <cmath>
#include <stack>
#include <limits>
#include <vector>
#include <bitset>
#include <string>
#include <cstdio>
#include <cstring>
#include <fstream>
#include <string.h>
#include <iostream>
#include <algorithm>
#define LL long long
#define Vi vector<int>
#define Si set<int>
#define readf freopen("input.txt","r",stdin)
#define writef freopen("output.txt","w",stdout)
#define FF(i,a) for(int i(0); i < (a); i++)
#define FD(i,a) for(int i(a); i >= (1); i--)
#define FOR(i,a,b) for(int i(a);i <= (b); i++)
#define FOD(i,a,b) for(int i(a);i >= (b); i--)
#define PD(a) printf("%d\n",a)
#define SET(a,b) memset(a,b,sizeof(a))
#define SD(a) scanf("%d",&(a))
#define LN printf("\n")
#define PS printf(" ")
#define pb push_back
#define lson l , m , rt << 1
#define rson m + 1 , r , rt << 1 | 1
const double pi = acos(-1.0);
const int maxn = 301;
const int INF = ~0U>>1;
const int dx[]={0,1,0,-1};
const int dy[]={1,0,-1,0};
using namespace std;
int A[maxn];
struct info
{
    int L,R,M,S;
    info(int x=0):L(x),R(x),M(x),S(x){}
}none;
info operator+(const info&l,const info&r)
{
    info f;
    if(l.M==-INF)   return r;
    if(r.M==-INF)   return l;
    f.L=max(l.L,l.S+r.L);
    f.R=max(r.R,r.S+l.R);
    f.S=l.S+r.S;
    f.M=max(l.M,r.M);
    f.M=max(f.M,l.R+r.L);
    return f;
}
info T[maxn*3];
inline void Set(int t,int x)
{
    T[t]=info(x);
}
void build(int t,int l,int r)
{
    if(l+1==r){
        Set(t,A[l]);
        return;
    }
    build(t*2,l,(l+r)/2);
    build(t*2+1,(l+r)/2,r);
    T[t]=T[t*2]+T[t*2+1];
}
void change(int t,int l,int r,int p,int s)
{
    if(l+1==r){
        Set(t,s);return;
    }
    if(p<(l+r)/2) change(t*2,l,(l+r)/2,p,s);
    else change(t*2+1,(l+r)/2,r,p,s);
    T[t]=T[t*2]+T[t*2+1];
}
info ask(int t,int l,int r,int a,int b)
{
    if(b<=l||a>=r) return none;
    if(l>=a&&r<=b) return T[t];
    return ask(t*2,l,(l+r)/2,a,b)+ask(t*2+1,(l+r)/2,r,a,b);
}
int main()
{
    none.M=-INF;
    int n,m,a,b,c;
    scanf("%d %d",&n,&m);
    FF(i,n)scanf("%d",A+i);
    build(1,0,n);
    while(m--)
    {
        scanf("%d %d %d",&a,&b,&c);
        if(a==1){
            if(b>c) swap(b,c);
            printf("%d\n",ask(1,0,n,b-1,c).M);
        }
        else change(1,0,n,b-1,c);
    }
}