# Best Time To Buy And Sell Stock Problem

## Description

LeetCode Problem 121.

You are given an array prices where prices[i] is the price of a given stock on the i^th 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:

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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:

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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 <= 10^5
- 0 <= prices[i] <= 10^4

## Sample C++ Code

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class Solution {
public:
int maxProfit(vector<int>& prices) {
if (prices.size() == 0)
return 0;
int pre_min = prices[0];
int max_profit = 0;
for (int i = 1; i < prices.size(); i ++) {
max_profit = max(max_profit, prices[i] - pre_min);
pre_min = min(pre_min, prices[i]);
}
return max_profit;
}
};