Recursion: Davis' Staircase

davis-staircase.js

//https://www.hackerrank.com/challenges/ctci-recursive-staircase

function stairStepper(stepSizes) {
    let answers = [1,1];
    return function(numSteps) {
        if(numSteps < 0) {
            return 0;
        }else if(typeof answers[numSteps] === 'undefined') {
            answers[numSteps] = stepSizes.reduce((totalSteps, stepSize) => totalSteps + stairCombinations(numSteps-stepSize), 0);
        }
        return answers[numSteps];
    };
}


const stairCombinations = stairStepper([1,2,3]);

[1,3,7, 10, 40].forEach(value => console.log(stairCombinations(value)));