POJ2299（归并排序）

#include <stdio.h>#include <stdlib.h>__int64 counter;void merge(long int A[],int p,int q,int r){int n1,n2,i,k,j,m=1,n=1;long int *L,*R;n1=q-p+1;n2=r-q;L=malloc((n1+2)*sizeof(int));R=malloc((n2+2)*sizeof(int));for (i=p;i<=q;i++)L[m++]=A[i];for (i=q+1;i<=r;i++)R[n++]=A[i];i=1;j=1;for (k=p;k<=r;k++){if ( (L[i]<=R[j] && i<=n1) || j>n2){A[k]=L[i];i++;}else{A[k]=R[j];counter+=n1-i+1;j++;}}free(L);free(R);}void mergesort(long int A[],int p,int r){int q;if (p<r){q=(p+r)/2;mergesort(A,p,q);mergesort(A,q+1,r);merge(A,p,q,r);}}int main(){long int A[500000];int i,size,p=1;while (1){counter=0;scanf("%d",&size);if (size==0)break;  for (i=1;i<=size;i++)  scanf("%ld",&A[i]);  mergesort(A,p,size);    printf("%I64d\n",counter);}return 0;}