Question

Can somebody tell me what is the longest flat subsection?

Answer 1

Given an array a[0:n) (n≧0), its subsection a[p,q) (0≦p≦q≦n) is called “flat” if ∀i,j:p≦i≦j＜q:a[i]＝a[j].

tranlsates to english as “a subsequence is considered flat if and only if all elements within the sequence are equal to each other”. Since equality is transitive, reflexive and symmetric, you can find it as:

pre: a is a sequence of symbols
     n is its length

last = null
bestAt = null
bestLen = -1
for each i in 0..n-1
  if a[i] != last
    thisAt = i
    thisLen = 1
    last=a[i]
    if thisLen > bestLen
      bestLen = thisLen
      bestAt = thisAt
  else
    thisLen++
  last=a[i]

post: a is not modified
      n is not modified
      bestAt holds the position of the first longest subsequence
      bestLen holds the length of the first longest subsequence