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61 lines
1.7 KiB
Plaintext
61 lines
1.7 KiB
Plaintext
---
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title: '121. Best Time to Buy and Sell Stock'
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description: You are given an array prices where prices[i] is the price of a given stock on the i^th day
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sidebar:
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label: 'Best Time to Buy and Sell Stock'
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badge: 'Easy'
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---
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<Badge variant="accent">Array</Badge>
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### Example 1:
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- Input: `prices = [7,1,5,3,6,4]`
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- Output: `5`
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- 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.
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### Example 2:
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- Input: `prices = [7,6,4,3,1]`
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- Output: `0`
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- Explanation: In this case, no transactions are done and the max profit = `0`.
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### Constraints:
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- `1 <= prices.length <= 10^5`
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- `0 <= prices[i] <= 10^4`
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## Approach
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::::warning
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The diagram traces the code below literally. That code does not run: `curr` and `ans` are never initialised, so the first `curr > left` test raises `NameError`, and `left` holds a price rather than an index, so `prices[left]` indexes by value.
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::::
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```mermaid
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flowchart TD
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S(["maxProfit(prices)"]) --> I["left = min(prices)"]
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I --> F{"more right in range(len(prices))?"}
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F -- no --> E(["return ans"])
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F -- yes --> W{"curr > left?"}
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W -- yes --> P["curr -= prices[left]; left += 1"]
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P --> W
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W -- no --> M["ans = max(ans, curr)"]
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M --> F
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```
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## Solution
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```py
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class Solution:
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def maxProfit(self, prices: List[int]) -> int:
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left = min(prices)
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for right in range(len(prices)):
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while curr > left:
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curr -= prices[left]
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left += 1
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ans = max(ans, curr)
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return ans
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```
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## Explanation
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<YouTube id="1pkOgXD63yU" title="Sliding Window: Best Time to Buy and Sell Stock - Leetcode 121 - Python" />
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