Why does a top-down computational parsing algorithm, using a context-free grammar, sometimes exhibit exponential time complexity when processing a highly ambiguous sentence?

💡 Explanation

The exponential time complexity arises because the top-down parser redundantly explores identical sub-parses for ambiguous sentence structures. This is because the parser re-computes parse trees rather than reusing previously computed results; therefore, time complexity increases exponentially rather than linearly, as seen with bottom-up methods.

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