上升子序列求和(dp经典)

Author: cls1991

DynamicProgramming/122_BestTimeToBuyAndSellStockII.py

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+# coding: utf8
+
+
+"""
+    题目链接: https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/description.
+    题目描述:
+
+    Say you have an array for which the ith element is the price of a given stock on day i.
+
+    Design an algorithm to find the maximum profit. You may complete as many transactions as you like (ie, buy one and
+    sell one share of the stock multiple times). However, you may not engage in multiple transactions at the same time
+    (ie, you must sell the stock before you buy again).
+
+"""
+
+
+class Solution(object):
+    def maxProfit(self, prices):
+        """
+        :type prices: List[int]
+        :rtype: int
+        """
+        if not prices:
+            return 0
+
+        return self.dynamic_max_profit(prices)
+
+    # 动态规划:
+    # 搜索所有的上升子序列, 求和
+    def dynamic_max_profit(self, prices):
+        ans = 0
+        start = 0
+        for i in range(1, len(prices)):
+            delta = prices[i] - prices[i - 1]
+            if delta < 0:
+                ans += prices[i - 1] - prices[start]
+                start = i
+
+        if prices[-1] > prices[start]:
+            ans += prices[-1] - prices[start]
+
+        return ans