Iterative run probability

ProbRun.js

// Probability of a r or more consecutive heads in n tosses
// of a coin having probability p of heads
// P(i) = P(i-1) + [1 - P(i-r-1)] * (1-p)p^r, for i > r
// P(r) = p^r
// P(i) = 0, for i < r
// where i is the flip.
// P is implemented as a circular array prob of size 0:r.
function ProbRun(n, r, p) {
	let prob = [r], iter, last, i, j;
	let c = (1 - p) * Math.pow(p, r);
	iter = n / (r + 1)
	last = Math.round(n - iter * (r + 1));
	c = (1 - p) * Math.pow(p, r);
	prob[r] = Math.pow(p, r);
	for (j = 1; j < iter; j++) {
		prob[0] = prob[r] + (1 - prob[0]) * c;
		for (i = 1; i < r; i++) {
			prob[i] = prob[i - 1] + (1 - prob[i]) * c
		}
	}
	return prob[last];
}