Finds the cumulative win probability of a target payout in bustabit/bustadice. Results parameter expects an ordered array of numbers representing the games bust history.

IterativeProb.js

/**
 * Calculates current cumulative geometric probability
 * @param payout Target payout to calculate for
 * @param results Array of ordered results
 * @param precision Num decimal places accuracy
 * @param debug Output result slice to console
 * @returns Cumulative geometric win probability
 */
function getCumulativeProb(payout, results, precision, debug = false) {
    let prc = 10 ** Math.max(1, Math.min((precision || 18), 18), 1);
    if (Array.isArray(results) && results.length) {
        for (let i = 0, j = results.length; i < j; i++) {
            if (results[j - i] >= payout) {
                let pmf = (1 - ((1 - (0.99 / payout)) ** i));
                let res = Math.min(1, Math.max(Math.round(pmf * prc) / prc, 0));
                (debug && console.debug(`${payout}x : ${res*100}% [${results.slice(-i)}](${i})`));
                return res;
            }
        }
    }
    return 0;
}