code: function summarizeContributions(contributions) {
    let busiestDay = null;
    let total = 0;
    contributions.forEach(d => {
      if (d.count > 0 && (!busiestDay || d.count > busiestDay.count)) {
        busiestDay = d;
      }
      total += d.count;
    });
    return {
      busiestDay,
      end: contributions.slice(-1)[0].date,
      start: contributions[0].date,
      total
    };
  }
docs: Summarize list of contribution
  
  @param {Array<{date: string, count: number}>} contributions - List of contribution
  @return {{end: string, start: string, total: number, busiestDay: {date: string, count: number}}}