Java 9 and IntSummaryStatistics et al.

[Chris Dennis]

This is indeed nice… but I presume that we all agree that the best solution here would be to allow instantiation of an IntSummaryStatistics object in a specific state.

> On Mar 29, 2017, at 2:43 PM, Peter Levart <peter.levart at gmail.com> wrote:
> 
> 
> 
> On 03/29/2017 06:06 PM, Chris Dennis wrote:
>> Remi: I really have to squint pretty hard to see that as anything other than “brute-force” - it’s still an O(N) calculation.
> 
> Here's O(log2(N)):
> 
>    static IntSummaryStatistics create(long count, long sum, int min, int max) {
>        if (count < 2 || min == max) {
>            return combineProduct(new IntSummaryStatistics(), count, min);
>        } else {
>            long minCnt = (count * max - sum) / (max - min);
>            long maxCnt = count - minCnt - 1;
>            long minSum = minCnt * min;
>            long maxSum = maxCnt * max;
>            long minMaxSum = minSum + maxSum;
>            int mid = (int) (sum - minMaxSum);
>            IntSummaryStatistics stats = new IntSummaryStatistics();
>            combineProduct(stats, minCnt, min);
>            combineProduct(stats, maxCnt, max);
>            stats.accept(mid);
>            return stats;
>        }
>    }
> 
>    static IntSummaryStatistics combineProduct(IntSummaryStatistics stats, long count, int value) {
>        IntSummaryStatistics pow2 = null;
>        while (count > 0) {
>            if (pow2 == null) {
>                pow2 = new IntSummaryStatistics();
>                pow2.accept(value);
>            } else {
>                pow2.combine(pow2);
>            }
>            if ((count & 1L) == 1L) {
>                stats.combine(pow2);
>            }
>            count >>>= 1;
>        }
>        return stats;
>    }
> 
> 
> Regards, Peter
>