hdu 1394 Minimum Inversion Number

http://acm.hdu.edu.cn/showproblem.php?pid=1394

 1 #include <cstdio>

 2 #include <cstring>

 3 #include <algorithm>

 4 #define maxn 50000

 5 using namespace std;

 6 

 7 struct node

 8 {

 9     int l,r;

10     int ans;

11 }tree[maxn*4];

12 

13 void build(int i,int l,int r)

14 {

15     tree[i].l=l;tree[i].r=r;

16     tree[i].ans=0;

17     if(l==r) return ;

18     int mid=(l+r)>>1;

19     build(i<<1,l,mid);

20     build(i<<1|1,mid+1,r);

21 }

22 

23 int search1(int i,int l,int r)

24 {

25     if(tree[i].l==l&&tree[i].r==r)

26     {

27         return tree[i].ans;

28     }

29     int mid=(tree[i].l+tree[i].r)>>1;

30     if(r<=mid)

31     {

32         return search1(i<<1,l,r);

33     }

34     else if(l>mid)

35     {

36         return search1(i<<1|1,l,r);

37     }

38     else

39     {

40         return search1(i<<1,l,mid)+search1(i<<1|1,mid+1,r);

41     }

42 }

43 

44 void update(int i,int c)

45 {

46     tree[i].ans++;

47     if(tree[i].l==tree[i].r) return ;

48     int mid=(tree[i].l+tree[i].r)>>1;

49     if(c<=mid)

50     {

51         update(i<<1,c);

52     }

53     else

54     {

55         update(i<<1|1,c);

56     }

57 }

58 

59 int main()

60 {

61     int a[maxn],n;

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

63     {

64         build(1,0,n-1);

65         int sum=0;

66         for(int i=1; i<=n; i++)

67         {

68             scanf("%d",&a[i]);

69             sum+=search1(1,a[i],n-1);

70             update(1,a[i]);

71         }

72         int cc=sum;

73         for(int i=1; i<=n; i++)

74         {

75             sum+=(-a[i]+n-a[i]-1);

76             cc=min(cc,sum);

77         }

78         printf("%d\n",cc);

79     }

80     return 0;

81 }

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