leetcode-97.js

var isInterleave = function(s1, s2, s3) {
  // caso trivial
  if (s3.length === 0) {
    return s1.length === 0 && s2.length === 0
  }
  
  // caso general
  let result1 = false, result2 = false
  if (s1.length > 0 && s3[0] === s1[0]) {
    result1 = isInterleave(s1.substring(1), s2, s3.substring(1))
  }
  
  if (s2.length > 0 && s3[0] === s2[0]) {
    result2 = isInterleave(s1, s2.substring(1), s3.substring(1))
  }
  
  return result1 || result2
}