16. 最接近的三数之和

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number}
 */
var threeSumClosest = function (nums, target) {
  let result
  let minGap = 0
  const len = nums.length
  if (nums === null || len < 3) {
    return result
  }
  nums.sort((a, b) => a - b)
  if (nums[0] > target) {
    result = nums[0] + nums[1] + nums[2]
  }
  for (let i = 0; i < nums.length - 2; i++) {
    let L = i + 1
    let R = len - 1
    while (L < R) {
      let sum = nums[i] + nums[L] + nums[R]
      let gap = Math.abs(sum - target)
      if (gap === 0) {
        result = sum
        break
      }
      if (gap < minGap || minGap === 0) {
        minGap = gap
        result = sum
      }
      sum > target ? R-- : L++
    }
  }
  return result
}