代码简单易懂

#include<bits/stdc++.h>
using namespace std;
const int MAX_N=200005;
int n,a[MAX_N],fl1[MAX_N],fr1[MAX_N],fl2[MAX_N],fr2[MAX_N],f1[MAX_N],f2[MAX_N],f3[MAX_N],f4[MAX_N],ans,ans1=0x7fffffff,ans2=0xffffffff;
int main(){
	memset(f1,0xcf,sizeof(f1));
	memset(f2,0xcf,sizeof(f2));
	memset(f3,0x3f,sizeof(f3));
	memset(f4,0x3f,sizeof(f4));
	memset(fl1,0xcf,sizeof(fl1));
	memset(fr1,0xcf,sizeof(fr1));
	memset(fl2,0x3f,sizeof(fl2));
	memset(fr2,0x3f,sizeof(fr2));
	scanf("%d",&n);
	for(int i=1;i<=n;i++){
		scanf("%d",&a[i]);
		ans+=a[i];
	}
	for(int i=1;i<=n;i++){
		f1[i]=max(f1[i-1]+a[i],a[i]);
		f3[i]=min(f3[i-1]+a[i],a[i]);
	}
	for(int i=n;i;i--){
		f2[i]=max(f2[i+1]+a[i],a[i]);
		f4[i]=min(f4[i+1]+a[i],a[i]);
	}
	for(int i=1;i<=n-2;i++){
		fl1[i]=max(fl1[i-1],f1[i]);
		fl2[i]=min(fl2[i-1],f3[i]);
	}
	for(int i=n;i>=3;i--){
		fr1[i]=max(fr1[i+1],f2[i]);
		fr2[i]=min(fr2[i+1],f4[i]);
	}
	for(int i=2;i<=n-1;i++){
		ans1=min(ans1,fl2[i-1]+fr2[i+1]);
		ans2=max(ans2,fl1[i-1]+fr1[i+1]);
	}
	ans=max(ans-ans1,ans2);
	printf("%d",ans);
	return 0;
}