HDU 3516 DP 四边形不等式优化 Tree Construction

设d(i, j)为连通第i个点到第j个点的树的最小长度，则有状态转移方程：

d(i, j) = min{ d(i, k) + d(k + 1, j) + p[k].y - p[j].y + p[k+1].x - p[i].x }

然后用四边形不等式优化之。。

 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 #include <map>
 #define MP make_pair
 #define x first
 #define y second
 using namespace std;

 typedef pair<int, int> PII;

 const int maxn =  + ;
 const int INF = 0x3f3f3f3f;
 int n;

 PII p[maxn];

 int d[maxn][maxn], s[maxn][maxn];

 int main()
 {
     while(scanf("%d", &n) ==  && n)
     {
         for(int i = ; i <= n; i++) scanf("%d%d", &p[i].x, &p[i].y);
         for(int i = ; i <= n; i++)
         {
             s[i][i + ] = i;
             d[i][i + ] = p[i+].x - p[i].x + p[i].y - p[i+].y;
         }

         for(int l = ; l <= n; l++)
         {
             for(int i = ; i + l -  <= n; i++)
             {
                 int j = i + l - ;
                 d[i][j] = INF;
                 for(int k = s[i][j-]; k <= s[i+][j]; k++)
                 {
                     int t = d[i][k] + d[k+][j] + p[k].y - p[j].y + p[k+].x - p[i].x;
                     if(t < d[i][j])
                     {
                         d[i][j] = t;
                         s[i][j] = k;
                     }
                 }
             }
         }

         printf("%d\n", d[][n]);
     }

     return ;
 }

代码君