二分查找

var search = function(nums, target) {
  if(!nums || !nums.length) {
    return -1
  }
  let left = 0;
  let right = nums.length
  while(left <= right) {
    // 避免超出最大数值
    let mid = Math.floor(left + (right - left) / 2)
    if(nums[mid] === target) {
      return mid
    } else if(nums[mid] < target) {
      // 此时mid可以排除在外，感谢一位面试官的提示😅
      left = mid + 1
    } else {
      right = mid - 1
    }
  }
  return - 1
};