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。

 1 #include <stdio.h>

 2 #include <string.h>

 3 

 4 #define N 500005

 5 int map[N], dp[N];

 6 

 7 int main ()

 8 {

 9     int x, y, n, i, j = 0;

10     

11     while (scanf ("%d", &n) != EOF)

12     {

13         for (i=0; i<n; i++)

14         {

15             scanf ("%d %d", &x, &y);

16             map[x] = y;

17         }

18         

19         memset (dp, 0, sizeof(dp));

20         

21         dp[1] = map[1];

22         

23         int low, up, mid, len = 1;

24         for (i=2; i<=n; i++)

25         {

26             low = 1;

27             up = len;

28             

29             while (low <= up)

30             {

31                 mid = (low + up) / 2;

32                 if (dp[mid] > map[i])

33                     up = mid - 1;

34                 else

35                     low = mid + 1;

36             }

37             

38             dp[low] = map[i];

39             if (low > len)

40                 len ++;

41         }

42         if (len == 1)

43             printf ("Case %d:\nMy king, at most 1 road can be built.\n\n", ++j);

44         else

45             printf ("Case %d:\nMy king, at most %d roads can be built.\n\n", ++j, len);

46     }

47     

48     return 0;

49 }

View Code