Best Time to Buy and Sell Stock.cpp

/*
Best Time to Buy and Sell Stock
=================================

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 <= 105
0 <= prices[i] <= 104
*/

class Solution
{
public:
  int maxProfit(vector<int> &prices)
  {
    int n = prices.size();
    if (n == 0)
      return 0;
    int ans = 0;
    int curr_min = prices[0];

    for (int i = 1; i < n; ++i)
    {
      if (prices[i] - curr_min > 0)
        ans = max(ans, prices[i] - curr_min);
      curr_min = min(curr_min, prices[i]);
    }

    return ans;
  }
};