正解 by harenz:

#include <bits/stdc++.h>
const int N=25010;
using namespace std;
typedef long long ll;
bool debug1;
int n;
int c[N],a[N],b[N];
struct node{
    int job,id,key;
} d[N];
bool debug2;
bool cmp(node x,node y){
    return x.key<y.key;
}
int main(){
    scanf("%d", &n);
    for(int i=1; i<=n; i++){
        scanf("%d%d", &a[i], &b[i]);
        d[i].id=i;
        if(a[i]<b[i]){
            d[i].job=1;
            d[i].key=a[i];
        }else
            d[i].key=b[i];
    }
    sort(d+1, d+n+1, cmp);
    ll j=1, k=n;
    for(int i=1; i<=n; i++)
        if(d[i].job)
            c[j++]=d[i].id;
        else
            c[k--]=d[i].id;
    j=a[c[1]];
    k=j+b[c[1]];
    for(int i=2; i<=n; i++){
        j+=a[c[i]];
        if(j<k)
            k+=b[c[i]];
        else
            k=j+b[c[i]];
    }
    printf("%lld", k);
    return 0;
}

错解 by hansang:

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;const int N=25e3+10;
struct node{LL x, y;} a[N];
bool cmp(node n1, node n2){
    LL t1=n1.x+max(n2.x, n1.y)+n2.y;
    LL t2=n2.x+max(n1.x, n2.y)+n1.y;
    return t1<t2;
}
int main(){
    int n; scanf("%d", &n);
    for(int i=1; i<=n; i++) scanf("%lld%lld", &a[i].x, &a[i].y);
    sort(a+1, a+n+1, cmp);
    LL ans=0, s1=0, s2=0;
    for(int i=1; i<=n; i++){
        s1+=a[i].x;
        if(s2<s1) s2=s1;
        s2+=a[i].y;
    }
    printf("%lld\n", max(s1, s2));
    return 0;
}

by harenz(正解):

#include <bits/stdc++.h>
const int N=25010;
using namespace std;
typedef long long ll;
bool debug1;
int n;
int c[N],a[N],b[N];
struct node{
	int job,id,key;
} d[N];
bool debug2;
bool cmp(node x,node y){
	return x.key<y.key;
}
int main(){
//	freopen("data.in","r",stdin);
//	freopen("my.out","w",stdout);
//	cout<<((&debug2-&debug1)/1024.0/1024.0)<<endl;
	scanf("%d",&n);
	for(int i=1;i<=n;i++){
		scanf("%d%d",&a[i],&b[i]);
		d[i].id=i;
		if(a[i]<b[i]){
			d[i].job=1;
			d[i].key=a[i];
		}else
			d[i].key=b[i];
	}
	sort(d+1,d+n+1,cmp);
	ll j=1,k=n;
	for(int i=1;i<=n;i++)
		if(d[i].job)
			c[j++]=d[i].id;
		else
			c[k--]=d[i].id;
	j=a[c[1]];
	k=j+b[c[1]];
	for(int i=2;i<=n;i++){
		j+=a[c[i]];
		if(j<k)
			k+=b[c[i]];
		else
			k=j+b[c[i]];
	}
	printf("%lld",k);
	return 0;
} 

by hansang(错解):

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
const int N=25e3+10;
struct node{LL x, y;} a[N];
bool cmp(node n1, node n2){
    LL t1=n1.x+max(n2.x, n1.y)+n2.y;
    LL t2=n2.x+max(n1.x, n2.y)+n1.y;
    return t1<t2;
}
int main(){
    int n; scanf("%d", &n);
    for(int i=1; i<=n; i++) scanf("%lld%lld", &a[i].x, &a[i].y);
    sort(a+1, a+n+1, cmp);
    LL ans=0, s1=0, s2=0;
    for(int i=1; i<=n; i++){
        s1+=a[i].x;
        if(s2<s1) s2=s1;
        s2+=a[i].y;
    }
    printf("%lld\n", max(s1, s2));
    return 0;
}