waysToClimbStairs.ts

// no recursion 
const waysToClimbStairs = (n:number):number => {
    const a:number[] = [1,1];
    if(n>1){
        for(let i = 2; i <= n ; i++){
            a[i] = a[i-1] + a[i-2];
        }
    };
    return a[a.length - 1];
}

// with recursion
const waysToClimbStairsRecursive = (n:number):number => {
    if (n < 0) return 0;
    if (n === 0) return 1;
    return waysToClimbStairsRecursive(n - 1) + waysToClimbStairsRecursive(n - 2);
}

// with recursion, but memoized 
const waysToClimbStairsRecursiveMemoized = (n:number, m:{ [key: number]: number } = {}):number => {
    if (n < 0) return 0;
    if (n === 0) return 1;
    if(m[n]) return n;
    return m[n] = waysToClimbStairsRecursiveMemoized(n - 1) + waysToClimbStairsRecursiveMemoized(n - 2);
}