= Solution
Track the length of the constant suffix of the scanned prefix:
``
best = 0; run = 0
for i = 0,...,n-1:
if i == 0 or a[i] != a[i-1]: run = 1
else: run = run+1
if run > best: best = run
return best
``
The condition is evaluated with short-circuit logic, so `a[-1]` is never accessed. After processing index $i$, `run` is the longest <constant segment of an array> ending there and `best` is the longest anywhere in $a[0:i+1)$. A maximal constant segment either extends the preceding suffix or starts at a changed value, proving the update. Empty input returns zero. Time is \b[$O(n)$], with constant auxiliary storage.
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