LeetCode #121. Best Time to Buy and Sell Stock

Time Complexity: O(n) - single pass through array
Space Complexity: O(1) - only using constant extra variables, no additional space used

class Solution {
    public int maxProfit(int[] prices) {
        int maxProfit = 0;
        int lowStockDay = prices[0];

        for (int i = 1; i < prices.length; i++) {
            if (prices[i] < lowStockDay)
                lowStockDay = prices[i];

            int profit = prices[i] - lowStockDay;

            if(maxProfit < profit)
                maxProfit = profit;
        }
        return maxProfit;
    }
}