Solve 'How many stairs will Suzuki climb in 20 years?'

[odv]

https://www.codewars.com/kata/how-many-stairs-will-suzuki-climb-in-20-years/train/javascript

Note: solve this also using flatMap(it will only work in browser), codewars or quokka don't support this yet so it is only for practicing.

[RazvanBugoi]

function stairsIn20(s){
  let sum = [];
  let output = 0;
  for (let i = 0; i < s.length; i += 1) {
    for (let j = 0; j < s[i].length; j += 1) {
      sum.push(s[i][j]);
    }
  }
 output += sum.reduce((current, prev) => current + prev) * 20;
 return output;
}