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.

class Solution {
    public int maxProfit(int[] prices) {
        var maxDiff = Integer.MIN_VALUE;
        for (int i = 0; i < prices.length; i ++) {
            for (int j = i + 1; j < prices.length; j ++) {
                maxDiff = Math.max(maxDiff, prices[j] - prices[i]);
            }   
        }
        return maxDiff < 0
            ? 0
            : maxDiff;
    }
}

import java.util.HashMap;
import java.util.Map;

class Solution {
    public int maxProfit(int[] prices) {
        var currentMinPrice = prices[0];
        var maxProfit = Integer.MIN_VALUE;
        for (int i = 1; i < prices.length; i ++) {
            var currentProfit = prices[i] - currentMinPrice;
            maxProfit = Math.max(maxProfit, currentProfit);
            currentMinPrice = Math.min(currentMinPrice, prices[i]);
        }
        return maxProfit < 0
            ? 0
            : maxProfit;
    }
}