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Replace All "aa"

AeroSpace • Anduril • cascading substring scrub

Remove every occurrence of "aa". Removals can create new pairs — continue until none remain. "baaabaaa" → "baba". Stack O(n) beats naive while "aa" in s: s.replace(...).

TimeO(n)

SpaceO(n)

i: —stack: ""pops: 0

Current char

Pair pop ("aa")

Stack kept

inputbaaabaaa

stack[ ]

Speed:

Ready

Press Play. Scan left→right; if top is a and current is a, pop (delete the pair).

Whiteboard

Size:3

Type It

Return the string after all "aa" pairs are gone (cascading — new pairs may form).

═══ REPLACE ALL "aa" ═══

PATTERN ▸ Stack scrub O(n)

① For each char c

if top=='a' and c=='a' → pop

else push c

② Join stack — no "aa" left

your implementation

Verify: