HDU1394（Minimum Inversion Number）

 1 #include <algorithm>
 2 #include <iostream>
 3 #include <sstream>
 4 #include <cstdlib>
 5 #include <cstring>
 6 #include <cstdio>
 7 #include <string>
 8 #include <bitset>
 9 #include <vector>
10 #include <queue>
11 #include <stack>
12 #include <cmath>
13 #include <list>
14 //#include <map>
15 #include <set>
16 using namespace std;
17 /***************************************/
18 #define ll long long
19 #define int64 __int64
20 #define PI 3.1415927
21 /***************************************/
22 const int INF = 0x7f7f7f7f;
23 const double eps = 1e-8;
24 const double PIE=acos(-1.0);
25 const int d1x[]= {0,-1,0,1};
26 const int d1y[]= {-1,0,1,0};
27 const int d2x[]= {0,-1,0,1};
28 const int d2y[]= {1,0,-1,0};
29 const int fx[]= {-1,-1,-1,0,0,1,1,1};
30 const int fy[]= {-1,0,1,-1,1,-1,0,1};
31 const int dirx[]= {-1,1,-2,2,-2,2,-1,1};
32 const int diry[]= {-2,-2,-1,-1,1,1,2,2};
33 /*vector <int>map[N];map[a].push_back(b);int len=map[v].size();*/
34 /***************************************/
35 void openfile()
36 {
37     freopen("data.in","rb",stdin);
38     freopen("data.out","wb",stdout);
39 }
40 priority_queue<int> qi1;
41 priority_queue<int, vector<int>, greater<int> >qi2;
42 /**********************华丽丽的分割线,以上为模板部分*****************/
43 const int M=5010;
44 int c[M];
45 int n;
46 int lowbit(int x)
47 {
48     return x&(-x);
49 }
50 int sum(int x)
51 {
52     int ret=0;
53     while(x>0)
54     {
55         ret+=c[x];
56         x-=lowbit(x);
57     }
58     return ret;
59 }
60 void add(int x,int val)
61 {
62     while(x<=n)
63     {
64         c[x]+=val;
65         x+=lowbit(x);
66     }
67 }
68 int main()
69 {
70     int a[M];
71     while(scanf("%d",&n)!=EOF)
72     {
73         int i,j;
74         int cnt=0;
75         memset(c,0,sizeof(c));
76         memset(a,0,sizeof(a));
77         for(i=0;i<n;i++)
78         {
79             scanf("%d",&a[i]);
80             a[i]++;
81             cnt+=sum(n)-sum(a[i]);
82             add(a[i],1);
83         }
84         int min=cnt;
85         for(int i=0;i<n;i++)
86         {
87             cnt+=n-a[i]-(a[i]-1);
88             if(cnt<min)
89                 min=cnt;
90         }
91         printf("%d\n",min);
92     }
93     return 0;
94 }