code: function computeLcsMatrix(xs, ys) {
    var n = xs.size||0;
    var m = ys.size||0;
    var a = makeMatrix(n + 1, m + 1, 0);
  
    for (var i = 0; i < n; i++) {
      for (var j = 0; j < m; j++) {
        if (Immutable.is(xs.get(i), ys.get(j))) {
          a[i + 1][j + 1] = a[i][j] + 1;
        }
        else {
          a[i + 1][j + 1] = Math.max(a[i + 1][j], a[i][j + 1]);
        }
      }
    }
  
    return a;
  }
docs: Computes the Longest Common Subsequence table
  @param xs Indexed Sequence 1
  @param ys Indexed Sequence 2