Question

Given this array

int [] myArray = {5,-11,2,3,14,5,-14,2};

I must be able to return 3 because the longest down sequence is 14,5,-14.
What’s the fastest way to do this?

PS: Down sequence is a series of non-increasing numbers.

Answer 1

Just make one pass through the list of numbers. Pseudocode:

bestIndex = 0
bestLength = 0

curIndex = 0
curLength = 1

for index = 1..length-1
   if a[index] is less than or equal to a[index-1]
       curLength++
   else 
       //restart at this index since it's a new possible starting point
       curLength = 1
       curIndex = index

   if curLength is better than bestLength
       bestIndex = curIndex
       bestLength = curLength

next          

Note: You can ditch any line containing bestIndex or curIndex if you don’t care about knowing where that subsequence occurs, as seen in Gary’s implementation.