题目大意：
求逆序对数，求循环移位后逆序数的最小值，意思一次将第一位移到最后一位，然后计算逆序对数，求出最小的那个。
解题思路：
数组数组。
代码：
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 ",min); 92 } 93 return 0; 94 }