poj2299 逆序數

        還是逆序數，之前那個DNA排序稍微改改就A了。

#include <stdio.h>#include <stdlib.h>#include <string.h>int a[500000];long long merge(int low,int mid,int high){long long count=0;if(low<high){int i=low;int j=mid;int k=0;int* tmp=(int*)malloc((high-low+1)*sizeof(int));while(i<mid&&j<=high){if(a[i]<=a[j]){tmp[k++]=a[i++];count+=(j-mid);}else{tmp[k++]=a[j++];}}while(i<mid){tmp[k++]=a[i++];count+=(high-mid+1);}while(j<=high){tmp[k++]=a[j++];}memcpy(a+low,tmp,(high-low+1)*sizeof(int));free(tmp);}return count;}long long inversion(int low,int high){long long count=0;if(low<high){int mid=(low+high)/2;count+=inversion(low,mid);count+=inversion(mid+1,high);count+=merge(low,mid+1,high);}return count;}int main(void){int N;int i;while(1){scanf("%d",&N);if(N==0){break;}for(i=0;i<N;i++){scanf("%d",a+i);}printf("%lld\n",inversion(0,N-1));}return 0;}