Simulating arknights banner pulls for W and Weedy.

arknightsPullCalc.js

let randomEntry = function(a) {
    let index = Math.floor(Math.random() * a.length);
    return a[index];
};

let count = function(a, test) {
    return a.reduce((counter, v) => {
        return counter + test(v); 
    }, 0);
};

let simulate = function() {
    let baseSixStarChance = 0.02;
    let numPulls = 0;
    let sixStarPityCounter = 0;

    let sixStarInfo = {
        rateUp: 0.7,
        chance: baseSixStarChance,
        rateUpOps: ['W', 'Weedy']
    };

    let opsPulled = [];

    let pull = function() {
        numPulls++;
        let p = Math.random();
        if (p < sixStarInfo.chance) {
            if (Math.random() < sixStarInfo.rateUp)
                opsPulled.push(randomEntry(sixStarInfo.rateUpOps));
            sixStarPityCounter = 0;
            sixStarInfo.chance = baseSixStarChance;
            return;
        }
        sixStarPityCounter++;
        if (sixStarPityCounter >= 50)
            sixStarInfo.chance += 0.02;
    };

    let redeemSparks = function() {
        if (!opsPulled.includes('Weedy')) {
            opsPulled.push('Weedy')
        } else if (!opsPulled.includes('W')) {
            opsPulled.push('W');
        }
    };

    while (!opsPulled.includes('W') || !opsPulled.includes('Weedy')) {
        pull();
        if (numPulls % 300 === 0) redeemSparks();
    }

    return numPulls;
};


let totalPulls = 0;
let pullCounts = [];
let simulationCount = 1000000;
for (let i = 0; i < simulationCount; i++) {
    let count = simulate();
    pullCounts.push(count);
    totalPulls += count;
}

console.log('Average pulls:', totalPulls / simulationCount);
for (let i = 10; i <= 300; i += 10) {
    let c =  100 * count(pullCounts, p => p <= i) / simulationCount;
    console.log(`Chance in ${i} pulls or less: ${c.toFixed(2)}%`);
}

output.txt

Average pulls: 141.943186
Chance in 10 pulls or less: 0.42%
Chance in 20 pulls or less: 1.64%
Chance in 30 pulls or less: 3.50%
Chance in 40 pulls or less: 5.87%
Chance in 50 pulls or less: 8.63%
Chance in 60 pulls or less: 12.52%
Chance in 70 pulls or less: 18.30%
Chance in 80 pulls or less: 24.19%
Chance in 90 pulls or less: 29.87%
Chance in 100 pulls or less: 35.27%
Chance in 110 pulls or less: 40.79%
Chance in 120 pulls or less: 47.18%
Chance in 130 pulls or less: 52.53%
Chance in 140 pulls or less: 57.07%
Chance in 150 pulls or less: 61.20%
Chance in 160 pulls or less: 64.99%
Chance in 170 pulls or less: 68.63%
Chance in 180 pulls or less: 72.11%
Chance in 190 pulls or less: 75.11%
Chance in 200 pulls or less: 77.71%
Chance in 210 pulls or less: 80.06%
Chance in 220 pulls or less: 82.17%
Chance in 230 pulls or less: 84.09%
Chance in 240 pulls or less: 85.87%
Chance in 250 pulls or less: 87.41%
Chance in 260 pulls or less: 88.77%
Chance in 270 pulls or less: 90.00%
Chance in 280 pulls or less: 91.08%
Chance in 290 pulls or less: 92.06%
Chance in 300 pulls or less: 99.97%