UVa 12004 Bubble Sort: Idea questions

http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem= 3155

Enumeration Exchange count is too troublesome, may wish to change the idea: for any pair of numbers, the probability of exchange between them and the probability of not exchanging is equal, that the expected value of the number is 1/2. There is a total of C (n,2) on the number, so the ultimate expectation is n (n-1)/4

Complete code:

01./*0.015s*/
.  
#include <cstdio>  
.  
05.int Main ()  
06.{    long x;  
"    int T", cas = 0;    scanf ("%d", &t);  
While    (t--)  
.    {        scanf ("%lld", &x);  
x        = x * (x-1) >> 1;        printf ("Case%d:", ++cas);        if (x & 1) printf ("%lld/2\n", x);        Else printf ("%lld\n", x >> 1);  
18.}

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