228. 汇总区间

/**
 * @param {number[]} nums
 * @return {string[]}
 */
var summaryRanges = function (nums) {
  if (nums.length === 0) return []
  const result = []
  let start = nums[0],
    end = nums[0]
  let gap = 1
  for (let i = 1; i <= nums.length; i++) {
    if (nums[i] === start + gap) {
      gap++
      end = nums[i]
      continue
    } else {
      result.push(start === end ? start + '' : start + '->' + end)
      start = end = nums[i]
      gap = 1
    }
  }
  return result
}