HDU 3516 Tree Construction

Posted 2020-08-29 Fighting Heart

区间$dp$，四边形优化。

#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<stack>
#include<ctime>
#include<iostream>
using namespace std;
typedef long long LL;
const double pi=acos(-1.0),eps=1e-10;
void File()
{
    freopen("D:\\in.txt","r",stdin);
    freopen("D:\\out.txt","w",stdout);
}
template <class T>
inline void read(T &x)
{
    char c = getchar();
    x = 0;
    while(!isdigit(c)) c = getchar();
    while(isdigit(c))
    {
        x = x * 10 + c - ‘0‘;
        c = getchar();
    }
}

int n;
int x[1100],y[1100],dp[1100][1100],f[1100][1100];

int main()
{
    while(~scanf("%d",&n))
    {
        for(int i=1;i<=n;i++) scanf("%d%d",&x[i],&y[i]);
        if(n==1) { printf("0\n"); continue; }

        for(int i=0;i<=n;i++) dp[i][i]=0;
        for(int i=1;i<n;i++)
        {
            dp[i][i+1]=y[i]-y[i+1]+x[i+1]-x[i];
            f[i][i+1]=i;
        }

        for(int len=3;len<=n;len++)
        {
            for(int st=1;st<=n&&st+len-1<=n;st++)
            {
                int en=st+len-1;
                dp[st][en]=0x7FFFFFFF;
                for(int j=f[st][en-1];j<=f[st+1][en];j++)
                {
                    if(dp[st][j]+dp[j+1][en]+y[j]-y[en]+x[j+1]-x[st]<dp[st][en])
                    {
                        dp[st][en]=dp[st][j]+dp[j+1][en]+y[j]-y[en]+x[j+1]-x[st];
                        f[st][en]=j;
                    }
                }
            }
        }

        printf("%d\n",dp[1][n]);
    }
    return 0;
}