範例程式碼 uva10810
//uva10810
#include<bits/stdc++.h>
using namespace std;
int temp[500000];
long long int mergesort(int a[], int x, int y, long long int k) {
if (y == x)
return k;
k = mergesort(a, x, (x+y)/2, k);
k = mergesort(a, (x+y)/2+1, y, k);
for (int i = x, i1 = (x+y)/2+1, j = (x+y)/2, j1 = y, l = 0;;) {
if (i>j && i1>j1)
break;
else {
if (i>j) {
while (i1 <= j1) temp[l] = a[i1], i1++, l++;
}
else if (i1>j1) {
while (i<=j) temp[l] = a[i], i++, l++;
}
else if (a[i] > a[i1]) {
temp[l] = a[i1], k+= (j-i+1), l++, i1++;
}
else if (a[i] < a[i1]) {
temp[l] = a[i], l++, i++;
}
}
}
for(int i = x, j = 0; i<=y; i++, j++)
a[i] = temp[j];
return k;
}
int main() {
int n, a[500000];
long long int k;
while( scanf("%d",&n) && n) {
k = 0;
for(int i = 0; i<n; i++)
scanf("%d", &a[i]);
k = mergesort(a, 0, n-1, k);
printf("%lld\n", k);
}
return 0;
}