longest-harmonious-subsequence.py

# Time:  O(n)
# Space: O(n)

# We define a harmonious array is an array where the difference 
# between its maximum value and its minimum value is exactly 1.
#
# Now, given an integer array, you need to find the length of its 
# longest harmonious subsequence among all its possible subsequences.
#
# Example 1:
# Input: [1,3,2,2,5,2,3,7]
# Output: 5
# Explanation: The longest harmonious subsequence is [3,2,2,2,3].
# Note: The length of the input array will not exceed 20,000.

class Solution(object):
    def findLHS(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        lookup = collections.defaultdict(int)
        result = 0
        for num in nums:
            lookup[num] += 1
            for diff in [-1, 1]:
                if (num + diff) in lookup:
                    result = max(result, lookup[num] + lookup[num + diff])
        return result