1. Best Time to Buy And Sell Stock

Description

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 <= 10^5
• 0 <= prices[i] <= 10^4

Approach

• If sell at any point lower than buy we put buy = sell setting new low

class Solution {
    public int maxProfit(int[] prices) {
        int buy = 0;
        int sell = 1;
        int maxProfit = 0;
        while (sell < prices.length) {
            if (prices[buy] < prices[sell]) {
                int profit = prices[sell] - prices[buy];
                maxProfit = Math.max(maxProfit, profit);
            } else {
                buy = sell;
            }
            sell++;
        }
 
        return maxProfit;
    }
}