为什么把所有特判删了就能过？
```c++
#include <iostream>
using namespace std;
const int N = 5e5+10, inf = 1010;
struct Segment_Tree{ int m, l, r, s; } st[N<<2]; // s:all, m:max, l:lmax, r:rmax
inline Segment_Tree merge(Segment_Tree a, Segment_Tree b) {
Segment_Tree ret;
ret.m = max(max(a.m, b.m), a.r+b.l);
ret.l = max(a.l, a.s+b.l);
ret.r = max(b.r, b.s+a.r);
ret.s = a.s+b.s;
return ret;
}
#define le (u<<1)
#define ri (u<<1|1)
int n, m, tn, a[N];
inline void build() {
for(tn=1;tn<=n+1;tn<<=1);
for(int i=1;i<=n;++i) st[i+tn] = {a[i], a[i], a[i], a[i]};
for(int u=tn-1;u;--u) st[u]=merge(st[le], st[ri]);
}
inline void update(int u, int v) {
u+=tn, st[u] = {v, v, v, v};
for(u>>=1;u;u>>=1) st[u]=merge(st[le], st[ri]);
}
inline int query(int l, int r) {
Segment_Tree ansl = {-inf,-inf,-inf,-inf};
Segment_Tree ansr = {-inf,-inf,-inf,-inf};
for(l+=tn-1,r+=tn+1;l^r^1;l>>=1,r>>=1) {
if(~l&1) ansl=merge(ansl, st[l^1]);
if(r&1) ansr=merge(st[r^1], ansr);
}
return merge(ansl, ansr).m;
}
int main() {
cin>>n>>m;
for(int i=1;i<=n;++i) cin>>a[i];
build();
while(m--) {
int k; cin>>k;
if(k==1) {
int a, b; cin>>a>>b;
if(a > b) swap(a, b);
cout<<query(a, b)<<"\n";
} else {
int p, s; cin>>p>>s;
update(p, s);
}
}
return 0;
}
```
by lateworker @ 2023-12-16 12:21:13
@[lateworker](/user/489661) 有没有可能特判不正确(？
by sfqxx1 @ 2023-12-16 12:40:25
@[sfqxx1](/user/934014) 有可能, 但为什么不特判也能过?
by lateworker @ 2023-12-16 12:56:29
@[lateworker](/user/489661) 或许这个程序已经是正解，不需要特判了吧。
by sfqxx1 @ 2023-12-16 12:58:29