leetcode 697[easy]---Degree of an Array

难度：easy

Given a non-empty array of non-negative integers nums, the degree of this array is defined as the maximum frequency of any one of its elements.

Your task is to find the smallest possible length of a (contiguous) subarray of nums, that has the same degree as nums.

Example 1:

Input: [1, 2, 2, 3, 1]Output: 2Explanation: The input array has a degree of 2 because both elements 1 and 2 appear twice.Of the subarrays that have the same degree:[1, 2, 2, 3, 1], [1, 2, 2, 3], [2, 2, 3, 1], [1, 2, 2], [2, 2, 3], [2, 2]The shortest length is 2. So return 2.

Example 2:

Input: [1,2,2,3,1,4,2]Output: 6

思路： 题目讲得不清不楚，花了些功夫才搞懂。找到所给list里面重复次数最多的那个数的重复次数，即为该list的degree。然后寻找与原list的degree相同的最短子list。也就是重复出现次数最多的那个数在原list中出现的位置的从最左到最右之间的片段。

            用enumerate() 遍历list，同时获取索引和对应的值，设计三个dictionary，left 用于存放每个element在list中第一次出现的索引，right用于存放每个element在list中最后出现的索引。count用于存放每个element出现的次数。

          最后遍历count，找到所有value=degree的key，取最小值。