getDoubleBondCount(vertices) {
    let doubleBondCount = 0;

    for (let i = 0; i < this.members.length; i++) {
      let atom = vertices[this.members[i]].value;

      if (atom.bondType === '=' || atom.branchBond === '=') {
        doubleBondCount++;
      }
    }

    return doubleBondCount;
  }
Get the number of double bonds inside this ring.

@param {Vertex[]} vertices An array of vertices associated with the current molecule.
@returns {Number} The number of double bonds inside this ring.