hdu 1025 Constructing Roads In JGShining's Kingdom

本题明白题意以后，就可以看出是让求最长上升子序列，但是不知道最长上升子序列的算法，用了很多YY的方法去做，最后还是超时，

因为普通算法时间复杂度为O(n*2)，去搜了题解，学习了一下，感觉不错，拿出来分享一下。

 #include <stdio.h>
 #include <string.h>

 #define N 500005
 int map[N], dp[N];

 int main ()
 {
     int x, y, n, i, j = ;

     while (scanf ("%d", &n) != EOF)
     {
         for (i=; i<n; i++)
         {
             scanf ("%d %d", &x, &y);
             map[x] = y;
         }

         memset (dp, , sizeof(dp));

         dp[] = map[];

         int low, up, mid, len = ;
         for (i=; i<=n; i++)
         {
             low = ;
             up = len;

             while (low <= up)
             {
                 mid = (low + up) / ;
                 if (dp[mid] > map[i])
                     up = mid - ;
                 else
                     low = mid + ;
             }

             dp[low] = map[i];
             if (low > len)
                 len ++;
         }
         if (len == )
             printf ("Case %d:\nMy king, at most 1 road can be built.\n\n", ++j);
         else
             printf ("Case %d:\nMy king, at most %d roads can be built.\n\n", ++j, len);
     }

     return ;
 }