LeetCode-697:Degree of an Array (度相同的最小子数组)
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Question
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
Note:
nums.length
will be between 1 and 50,000.nums[i]
will be an integer between 0 and 49,999.
问题解析:
给定非空非负整数数组,数组的度是指数组中出现次数最多元素的个数。寻找最小连续子数组,使得子数组的度与原数组的度相同。返回子数组的长度。
Answer
Solution 1:
利用数据结构实现,Map、Dict。
- maxs记录元素的最大下标,mins记录元素的最小下标,cnts记录元素的出现个数,三者均是HashMap结构;
- 通过遍历记录元素与上三个对应的记录,只要找到最大次数对应的元素,则就找到了该元素的最大和最小下标,即找到了度相同的最小子数组。
class Solution { public int findShortestSubArray(int[] nums) { Map<Integer, Integer> start = new HashMap<Integer, Integer>(); Map<Integer, Integer> end = new HashMap<Integer, Integer>(); Map<Integer, Integer> count = new HashMap<Integer, Integer>(); int maxCount = 0; for (int i = 0; i < nums.length; i++){ if (!count.containsKey(nums[i])){ count.put(nums[i], 0); start.put(nums[i], i); } count.put(nums[i], count.get(nums[i])+1); end.put(nums[i], i); maxCount = Math.max(maxCount, count.get(nums[i])); } int minLength = Integer.MAX_VALUE; for (Integer key : count.keySet()){ if (count.get(key) == maxCount){ minLength = Math.min(minLength,end.get(key)-start.get(key)+1); } } return minLength; }}
- Runtime: 82 ms
- Beats 28.81 % of java submissions
- 时间复杂度:O(n);空间复杂度:O(1)
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