great solution :D
thanks.
On Wed, Feb 22, 2012 at 12:41 AM, sunny agrawal <sunny816.i...@gmail.com>wrote:
> we need to find how many sums are less than candidate Sum chosen in one
> iteration of binary search in range 0-S
> To count this, for each i we try to find how many sums ending at i are
> lesser than candidate sum !!
>
> lets say for some i-1 sum[0 - i-1] < candidate sum then we can say that
> i*(i-1)/2 sums are less than candidate sum.
> now lets say after adding a[i] again sum[0 - i] < candidateSum then u can
> add (i+1) to previous count because all sums [0 - i], sum[1 - i],
> ............. sum[i - i] will be lesser than candidate sum
> or if adding a[i] causes sum[0 - i] > candidateSum then u have to find a
> index g such that sum[g - i] < candidate sum, and increase the count by
> ((i)-(g) +1).
>
> eg lets say your candidate sum is 7 (for the given example{1,2,3,4,5}) k =
> 3 n = 5
> initially g = 0
> sum = 0;
> candidateSum = 7;
> count = 0
> iteration one:
> sum[0 - 0] = 1 < 7 so count += 0-0+1;
>
> iteration 2
> sum[0-1] = 3 < 7, count += 1-0+1
>
> iteration 3
> sum[0-2] = 6 < 7 count += 2-0+1;
>
> iteration 4
> sum[0,3] = 10 > 7 so now increment g such that sum[g,i] < 7
> so g = 3 count += 3-3+1;
>
> iteration 5
> sum[3 - 4] = 9 > 7
> new g = 4 count += 4-4+1
>
> final count = 8, so there are 8 sums less than 7
>
>
>
> On Wed, Feb 22, 2012 at 12:16 AM, shady <sinv...@gmail.com> wrote:
>
>> didn't get you, how to check for subsequences which doesn't start from
>> the beginning ? can you explain for that same example... should we check
>> for all contiguous subsequences of some particular length?
>>
>>
>> On Tue, Feb 21, 2012 at 11:15 PM, sunny agrawal
>> <sunny816.i...@gmail.com>wrote:
>>
>>> i dont know if a better solution exists
>>> but here is one with complexity O(N*logS)...
>>> N = no of elements in array
>>> S = max sum of a subarray that is sum of all the elements as all are
>>> positive
>>>
>>> algo goes as follows
>>> do a binary search in range 0-S, for each such candidate sum find how
>>> many sums are smaller than candidate sum
>>>
>>> there is also need to take care of some cases when there are exactly k-1
>>> sums less than candidate sum, but there is no contigious where sum =
>>> candidate sum.
>>>
>>>
>>> On Tue, Feb 21, 2012 at 11:02 PM, shady <sinv...@gmail.com> wrote:
>>>
>>>> Problem link <http://www.spoj.pl/ABACUS12/status/ABA12E/>
>>>>
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>>>
>>>
>>>
>>> --
>>> Sunny Aggrawal
>>> B.Tech. V year,CSI
>>> Indian Institute Of Technology,Roorkee
>>>
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>>
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>
>
>
> --
> Sunny Aggrawal
> B.Tech. V year,CSI
> Indian Institute Of Technology,Roorkee
>
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