step

by Paco86

JavaScript

function step(n, arr=[]){
	if(n < 0){
  	return 0;
  }else if(n === 0){
  	return 1;
  }else if(arr[n] !== undefined){
  	return arr[n];
  }else{
  	arr[n] = step(n-1, arr) + step(n-2, arr) + step(n-3, arr);
    
    return arr[n]
  }
}

console.log(step(100));