delete-and-earn.py

# Time:  O(n)
# Space: O(1)

# Given an array nums of integers, you can perform operations on the array.
#
# In each operation, you pick any nums[i] and delete it to earn nums[i] points.
# After, you must delete every element equal to nums[i] - 1 or nums[i] + 1.
#
# You start with 0 points.
# Return the maximum number of points you can earn by applying such operations.
#
# Example 1:
# Input: nums = [3, 4, 2]
# Output: 6
# Explanation: 
# Delete 4 to earn 4 points, consequently 3 is also deleted.
# Then, delete 2 to earn 2 points. 6 total points are earned.
#
# Example 2:
# Input: nums = [2, 2, 3, 3, 3, 4]
# Output: 9
# Explanation: 
# Delete 3 to earn 3 points, deleting both 2's and the 4.
# Then, delete 3 again to earn 3 points, and 3 again to earn 3 points.
# 9 total points are earned.
#
# Note:
# - The length of nums is at most 20000.
# - Each element nums[i] is an integer in the range [1, 10000].

class Solution(object):
    def deleteAndEarn(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        vals = [0] * 10001
        for num in nums:
            vals[num] += num
        val_i, val_i_1 = vals[0], 0
        for i in xrange(1, len(vals)):
            val_i_1, val_i_2 = val_i, val_i_1
            val_i = max(vals[i] + val_i_2, val_i_1)
        return val_i