归并排序！！！！！！！！！！
1 /* 2 归并排序+求逆序数 3 */ 4 #include<stdio.h> 5 #include<string.h> 6 #include<algorithm> 7 #include<stdlib.h> 8 using namespace std; 9 typedef __int64 int64; 10 const int maxn = 500005; 11 int64 a[ maxn ],Sort[ maxn ]; 12 int64 res; 13 14 void init(){ 15 res = 0; 16 } 17 18 void merge( int L,int R ){ 19 int mid = (L+R)/2; 20 int i = L; 21 int j = mid+1; 22 int pos = L; 23 while( i<=mid&&j<=R ){ 24 if( a[i]<a[j] ) 25 Sort[ pos++ ] = a[i++]; 26 else{ 27 Sort[ pos++ ] = a[j++]; 28 res += (mid-i+1); 29 } 30 } 31 while( i<=mid ) 32 Sort[ pos++ ] = a[i++]; 33 while( j<=R ) 34 Sort[ pos++ ] = a[j++]; 35 for( int k=L;k<=R;k++ ) 36 a[k] = Sort[k]; 37 } 38 39 void merge_sort( int L,int R ){ 40 int mid = (L+R)/2; 41 if( L<R ){ 42 merge_sort( L,mid ); 43 merge_sort( mid+1,R ); 44 merge( L,R ); 45 } 46 return ; 47 } 48 49 int main(){ 50 int n; 51 while( scanf("%d",&n),n ){ 52 for( int i=1;i<=n;i++ ) 53 scanf("%I64d",&a[i]); 54 init(); 55 merge_sort( 1,n ); 56 printf("%I64d ",res); 57 } 58 return 0; 59 }