一天一大 leet(魔术索引)难度:简单-Day20200731

输入：nums = [0, 2, 3, 4, 5]
输出：0
说明: 0下标的元素为0

输入：nums = [1, 1, 1]
输出：

/**
 * @param {number[]} nums
 * @return {number}
 */
var findMagicIndex = function (nums) {
  for (let i = 0; i < nums.length; i++) {
    if (i === nums[i]) return i
  }
  return -1
}

/**
 * @param {number[]} nums
 * @return {number}
 */
var findMagicIndex = function (nums) {
  function getAnswer(nums, left, right) {
    if (left > right) return -1
    let mid = parseInt((right - left) / 2, 10) + left
    let leftAnswer = getAnswer(nums, left, mid - 1)
    if (leftAnswer !== -1) {
      return leftAnswer
    } else if (nums[mid] === mid) {
      return mid
    }
    return getAnswer(nums, mid + 1, right)
  }
  return getAnswer(nums, 0, nums.length - 1)
}