求十亿个64位整数的平均数

int64 u = 10亿;

int64 a = 0,  b = 0;

for each  x in 10亿个数

{
if ( x >= u ) {

b += x/u;

x = x%u;

}

a += x;

if ( a >= u ) {

b += a/u;

a = a%u;
}
}

average = b + a/10亿;