查找

参考：
https://juejin.cn/post/6844903955252805645 。
https://juejin.cn/post/6844903866610221064 。

查找和排序都是在程序设计中经常用到的算法。查找相对而言较为简单，排序比查找要复杂一些。

查找有顺序查找、二分查找、哈希表查找、二叉排序树查找等。

顺序查找

直接 for 循环顺序查找效率最高。

二分查找

var searchRange = function (nums, target) {
  let left = 0;
  let mid;
  let right = nums.length;
  while (left < right) {
    mid = (left + right) >>> 1;
    if (nums[mid] > target) {
      right = mid;
    } else if (nums[mid] < target) {
      left = mid + 1;
    } else if (nums[mid] == target) {
      right = mid;
    }
  }
  let leftIndex = -1,
    rightIndex = -1;
  if (left == nums.length) return [-1, -1];
  else leftIndex = nums[left] == target ? left : -1;

  left = 0;
  right = nums.length;
  while (left < right) {
    mid = (left + right) >>> 1;
    if (nums[mid] > target) {
      right = mid;
    } else if (nums[mid] < target) {
      left = mid + 1;
    } else if (nums[mid] == target) {
      left = mid + 1;
    }
  }
  if (left == 0) return [-1, -1];
  else rightIndex = nums[left - 1] == target ? left - 1 : -1;
  return [leftIndex, rightIndex];
};