Developer Builds Browser-Based Lottery Combination Calculator Using Combinatorics

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A software developer built a lightweight, browser-based lottery bet calculator after a friend asked how many combinations arise from selecting extra numbers in a Chinese lottery game. The tool handles two betting modes: standard compound bets and the more complex 'dan-tuo' system, where certain numbers are locked into every combination. To avoid integer overflow in JavaScript, the developer used a multiplicative formula that keeps intermediate values manageable without relying on BigInt. AI assistance generated a working first draft quickly, though it contained a logic error in the dan-tuo calculation that required manual correction. The final tool runs entirely in HTML, CSS, and JavaScript with no dependencies or installation needed.

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