Function to parse domino strings.

domino.js

/*
Given a string, representing domino tiles chain. Each tile has L-R format, where L and R are numbers from 1..6 range. Tiles are separated by the comma. Some examples of valid S chain are:

1. 1-4,4-2,3-1
2. 6-3
3. 4-3,5-1,2-2,1-3,4-4

Devise a function that, give  a domino string, returns the number of tiles in the longest matching group within S. A matching group is a set of tiles that match and that are subsequent in S. Domino tiles match, if the right side of a tile is the same as the left side of the following tile. 2-4,4-1 are matching tiles, but 5-2,1-6 are not.

domino("1-1,3-5,5-2,2-3,2-4") should return 3.
*/

function domino(s) {
  var a = s.split(",");
  if (a.length == 0) return 0;
  var length = 0;
  var currentLength = 1;
  var lastR = 0;
  a.forEach(function(d) {
    var da = d.split("-");
    var l = da[0];
    var r = da[1];
    if (l == lastR) {
      currentLength++;
    } else {
      if (currentLength > length) length = currentLength;
      currentLength = 1;
    }
    lastR = r;
    if (currentLength > length) length = currentLength;
    //console.log(d,currentLength,length);
  });
  return length;

}

console.log(domino("1-1")); // 1
console.log(domino("1-2,1-2")); // 1
console.log(domino("3-2,2-1,1-4,4-4,5-4,4-2,2-1")); // 4
console.log(domino("5-5,5-5,4-4,5-5,5-5,5-5,5-5,5-5,5-5,5-5")); // 7