[BZOJ4247]挂饰(DP)

当最终挂饰集合确定了，一定是先挂挂钩多的在挂挂钩少的。

于是按挂钩从大到小排序，然后就是简单的01背包。

#include<cstdio>
#include<algorithm>
#define rep(i,l,r) for (int i=(l); i<=(r); i++)
using namespace std;

const int N=2010,inf=1e9;
int f[N][N];
int n,ans=-inf,v,c;
struct P{ int v,c; }s[N];
bool operator <(const P &a,const P &b){ return a.v>b.v; }

int main(){
    freopen("bzoj4247.in","r",stdin);
    freopen("bzoj4247.out","w",stdout);
    scanf("%d",&n);
    rep(i,1,n) scanf("%d%d",&s[i].v,&s[i].c);
    rep(i,0,n) f[0][i]=f[i][n+1]=-inf;
    f[0][1]=0; sort(s+1,s+n+1);
    rep(i,1,n) rep(j,0,n) f[i][j]=max(f[i-1][max(j-s[i].v,0)+1]+s[i].c,f[i-1][j]);
    rep(i,0,n) ans=max(ans,f[n][i]);
    printf("%d\n",ans);
    return 0;
}