bzoj1237

题解：

dp

显然置换不会超过3个

代码：

#include<bits/stdc++.h> 
using namespace std;
const int N=100005;
typedef long long ll;
int n,a[N],b[N];
ll inf,f[N];
int Abs(int x){return (x>0)?x:-x;}
ll calc(int x,int y)
{
    if (x==y) return inf;
    return (ll)Abs(x-y);
}
int main()
{
    scanf("%d",&n);
    for (int i=1;i<=n;i++)scanf("%d%d",&a[i],&b[i]);
    sort(a+1,a+n+1);sort(b+1,b+n+1);
    memset(f,127,sizeof(f));
    inf=f[0];f[0]=0;
    for (int i=1;i<=n;++i)
     {
        ll x,y,z;
        if (f[i-1]!=inf)
         {
            x=calc(a[i],b[i]);
            if (x!=inf) f[i]=min(f[i],f[i-1]+x);
         }
        if (i>=2)
         {
            x=calc(a[i],b[i-1]),y=calc(a[i-1],b[i]);
            if (x!=inf&&y!=inf) f[i]=min(f[i],f[i-2]+x+y);
         }
        if (i>=3)
         {
            x=calc(a[i-2],b[i]),y=calc(a[i-1],b[i-1]),z=calc(a[i],b[i-2]);
            if (x!=inf&&y!=inf&&z!=inf) f[i]=min(f[i],f[i-3]+x+y+z);
            x=calc(a[i-2],b[i-1]),y=calc(a[i-1],b[i]),z=calc(a[i],b[i-2]);
            if (x!=inf&&y!=inf&&z!=inf) f[i]=min(f[i],f[i-3]+x+y+z);
            x=calc(a[i-2],b[i]),y=calc(a[i-1],b[i-2]),z=calc(a[i],b[i-1]);
            if (x!=inf&&y!=inf&&z!=inf) f[i]=min(f[i],f[i-3]+x+y+z);
         }
     }
    printf("%lld
",f[n]);
}