old_contents: # Time:  O(R), R is the range size of the integers
  # Space: O(R)
  
  # Given an array of 2n integers, your task is to group these integers into n pairs of integer,
  # say (a1, b1), (a2, b2), ..., (an, bn) which makes sum of min(ai, bi) for all i from 1 to n as large as possible.
  #
  # Example 1:
  # Input: [1,4,3,2]
  #
  # Output: 4
  # Explanation: n is 2, and the maximum sum of pairs is 4.
  # Note:
  # n is a positive integer, which is in the range of [1, 10000].
  # All the integers in the array will be in the range of [-10000, 10000].
  
  class Solution(object):
      def arrayPairSum(self, nums):
          """
          :type nums: List[int]
          :rtype: int
          """
          LEFT, RIGHT = -10000, 10000
          lookup = [0] * (RIGHT-LEFT+1)
          for num in nums:
              lookup[num-LEFT] += 1
          r, result = 0, 0
          for i in xrange(LEFT, RIGHT+1):
              result += (lookup[i-LEFT] + 1 - r) / 2 * i
              r = (lookup[i-LEFT] + r) % 2
          return result
  
  # Time:  O(nlogn)
  # Space: O(1)
  class Solution2(object):
      def arrayPairSum(self, nums):
          """
          :type nums: List[int]
          :rtype: int
          """
          nums.sort()
          result = 0
          for i in xrange(0, len(nums), 2):
              result += nums[i]
          return result
  
new_contents: # Time:  O(r), r is the range size of the integers
  # Space: O(r)
  
  # Given an array of 2n integers, your task is to group these integers into n pairs of integer,
  # say (a1, b1), (a2, b2), ..., (an, bn) which makes sum of min(ai, bi) for all i from 1 to n as large as possible.
  #
  # Example 1:
  # Input: [1,4,3,2]
  #
  # Output: 4
  # Explanation: n is 2, and the maximum sum of pairs is 4.
  # Note:
  # n is a positive integer, which is in the range of [1, 10000].
  # All the integers in the array will be in the range of [-10000, 10000].
  
  class Solution(object):
      def arrayPairSum(self, nums):
          """
          :type nums: List[int]
          :rtype: int
          """
          LEFT, RIGHT = -10000, 10000
          lookup = [0] * (RIGHT-LEFT+1)
          for num in nums:
              lookup[num-LEFT] += 1
          r, result = 0, 0
          for i in xrange(LEFT, RIGHT+1):
              result += (lookup[i-LEFT] + 1 - r) / 2 * i
              r = (lookup[i-LEFT] + r) % 2
          return result
  
  # Time:  O(nlogn)
  # Space: O(1)
  class Solution2(object):
      def arrayPairSum(self, nums):
          """
          :type nums: List[int]
          :rtype: int
          """
          nums.sort()
          result = 0
          for i in xrange(0, len(nums), 2):
              result += nums[i]
          return result
  
subject: Update array-partition-i.py