Generating then filtering is O(2^(2n)) and wasteful. Backtracking with two counters builds only valid strings by enforcing the balance rule at every step. Here is the template and why the pruning conditions are exactly right.
Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.
Generating then filtering is O(2^(2n)) and wasteful. Backtracking with two counters builds only valid strings by enforcing the balance rule at every step. Here is the template and why the pruning conditions are exactly right.
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