LeetCode-in-All
121. Best Time to Buy and Sell Stock
Easy
You are given an array prices where prices[i] is the price of a given stock on the ith day.
You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock.
Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return 0.
Example 1:
Input: prices = [7,1,5,3,6,4]
Output: 5
Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.
Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell.
Example 2:
Input: prices = [7,6,4,3,1]
Output: 0
Explanation: In this case, no transactions are done and the max profit = 0.
Constraints:
1 <= prices.length <= 1050 <= prices[i] <= 104
Solution
defmodule Solution do
@spec max_profit(prices :: [integer]) :: integer
def max_profit(prices) do
max_profit_helper(prices, 0, :math.pow(2, 63))
end
defp max_profit_helper([], max_so_far, _cur_min), do: max_so_far
defp max_profit_helper([head | tail], max_so_far, cur_min) do
new_max_so_far = if head - cur_min > max_so_far, do: head - cur_min, else: max_so_far
new_cur_min = if head < cur_min, do: head, else: cur_min
max_profit_helper(tail, new_max_so_far, new_cur_min)
end
end