Maximum Profit From Trading Stocks — Python

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

import itertools


# dp, optimized from solution2
class Solution(object):
    def maximumProfit(self, present, future, budget):
        """
        :type present: List[int]
        :type future: List[int]
        :type budget: int
        :rtype: int
        """
        dp = [0]*(budget+1)
        for i, (p, f) in enumerate(itertools.izip(present, future)):
            if f-p < 0:
                continue
            for b in reversed(xrange(p, budget+1)):
                dp[b] = max(dp[b], dp[b-p]+(f-p))
        return dp[-1]


# Time:  O(n * b)
# Space: O(b)
import itertools


# dp
class Solution2(object):
    def maximumProfit(self, present, future, budget):
        """
        :type present: List[int]
        :type future: List[int]
        :type budget: int
        :rtype: int
        """
        dp = [[0]*(budget+1) for _ in xrange(2)]
        for i, (p, f) in enumerate(itertools.izip(present, future)):
            for b in xrange(budget+1):
                dp[(i+1)%2][b] = max(dp[i%2][b], (dp[i%2][b-p]+(f-p) if b-p >= 0 else 0))
        return dp[len(present)%2][-1]