leetcode （Degree of an Array）

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Title：Longest Continuous Increasing Subsequence    697

Difficulty：Easy

原题leetcode地址：https://leetcode.com/problems/degree-of-an-array/

1.  Map的Key的唯一性，Value不断的更新

时间复杂度：O(n)，两次一层for循环，遍历整个数组。

空间复杂度：O(n)，申请额外的3个Map空间。

    /**
     * 本题不难，需要巧妙的应用Map的特性：Key唯一，Value更新
     * getOrDefault()
     * Collections.max()
     * Map的Key的遍历
     * @param nums
     * @return
     */
    public static int findShortestSubArray(int[] nums) {

        Map<Integer, Integer> begin = new HashMap<>();
        Map<Integer, Integer> end = new HashMap<>();
        Map<Integer, Integer> count = new HashMap<>();

        for (int i = 0; i < nums.length; i++) {
            if (begin.get(nums[i]) == null) {
                begin.put(nums[i], i);
            }
            end.put(nums[i], i);
            count.put(nums[i], count.getOrDefault(nums[i], 0) + 1);
        }

        int min = nums.length;
        int degree = Collections.max(count.values());

        for (int key : count.keySet()) {
            if (count.get(key) == degree) {
                min = Math.min(min, end.get(key) - begin.get(key) + 1);
            }
        }

        return min;

    }