URAL 1078. Segments(DP)

题目链接

找出最高一个线段覆盖吧，很明显的O(n^2)的DP，注意排序的时候按长度排序。WA了一次，没有注意到题目中their endpoints do not coincide，他们的端点不能重合，我还以为输出要顺序有错误。。。得亏又看了遍题目。。

 1 #include <stdio.h>

 2 #include <string.h>

 3 #include <stdlib.h>

 4 struct segment

 5 {

 6     int x,y,len;

 7     int num;

 8 }p[501];

 9 int o[501],k[501],q[501];

10 int cmp(const void *a,const void *b)

11 {

12     return (*(struct segment *)a).len > (*(struct segment *)b).len?1:-1;

13 }

14 int main()

15 {

16     int i,j,n,t,max;

17     scanf("%d",&n);

18     for(i = 0;i <= n-1;i ++)

19     {

20         scanf("%d%d",&p[i].x,&p[i].y);

21         p[i].len = p[i].y-p[i].x;

22         p[i].num = i;

23     }

24     qsort(p,n,sizeof(p[0]),cmp);

25     o[0] = 1;k[0] = 0;

26     for(i = 1;i <= n-1;i ++)

27     {

28         max = 0;t = i;

29         for(j = 0;j <= i-1;j ++)

30         {

31             if(p[i].x < p[j].x&&p[i].y > p[j].y)

32             {

33                 if(o[j] > max)

34                 {

35                     max = o[j];

36                     t = j;

37                 }

38             }

39         }

40         o[i] = max+1;

41         k[i] = t;

42     }

43     max = 0;t = 0;

44     for(i = 0;i <= n-1;i ++)

45     {

46         if(max < o[i])

47         {

48             max = o[i];

49             t = i;

50         }

51     }

52     printf("%d\n",max);

53     for(i = 1;i <= max;i ++)

54     {

55         q[i] = p[t].num+1;

56         t = k[t];

57     }

58     for(i = max;i >= 1;i --)

59     {

60         if(i == max)

61         printf("%d",q[i]);

62         else

63         printf(" %d",q[i]);

64     }

65     printf("\n");

66     return 0;

67 }