POJ 3368 Frequent values(rmq)

题目链接

离散化后rmq，新白书上对这个题有讲解。

 1 #include <iostream>

 2 #include <cstring>

 3 #include <cmath>

 4 #include <cstdio>

 5 using namespace std;

 6 #define N  100000

 7 int p[N];

 8 int dp[22][N+1];

 9 int hash[3*N];

10 int que[N+1];

11 int L[N+1];

12 int R[N+1];

13 int o[N+1];

14 void init_rmq(int n)

15 {

16     int i,j;

17     for(i = 1;i <= n;i ++)

18     dp[0][i] = o[i];

19     for(i = 1;(1<<i) <= n;i ++)

20     {

21         for(j = 1;j + (1<<(i-1)) <= n;j ++)

22         {

23             dp[i][j] = max(dp[i-1][j],dp[i-1][j+(1<<(i-1))]);

24         }

25     }

26 }

27 int rmq(int x,int y)

28 {

29     if(x > y) return 0;

30     int k = log(y-x+1.0)/log(2.0);

31     return max(dp[k][x],dp[k][y-(1<<k)+1]);

32 }

33 int query(int x,int y)

34 {

35     int temp,nx,ny;

36     if(p[x] == p[y])

37     return y-x+1;

38     nx = hash[p[x]+N];

39     ny = hash[p[y]+N];

40     temp = max(R[nx]-x+1,y-L[ny]+1);

41     temp = max(temp,rmq(nx+1,ny-1));

42     return temp;

43 }

44 int main()

45 {

46     int n,m,i,temp,num,x,y;

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

48     {

49         if(n == 0) break;

50         scanf("%d",&m);

51         for(i = 1;i <= n;i ++)

52         {

53             scanf("%d",&p[i]);

54         }

55         L[1] = 1;

56         num = 1;

57         temp = 1;

58         hash[p[1]+N] = 1;

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

60         {

61             if(p[i] != p[i-1])

62             {

63                 R[num] = i-1;

64                 o[num] = temp;

65                 hash[p[i-1]+N] = num;

66                 temp = 1;

67                 num ++;

68                 L[num] = i;

69             }

70             else

71             {

72                 temp ++;

73             }

74         }

75         R[num] = i-1;

76         o[num] = temp;

77         hash[p[i-1]+N] = num;

78         init_rmq(num);

79         while(m--)

80         {

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

82             printf("%d\n",query(x,y));

83         }

84     }

85     return 0;

86 }