Best Time to Buy and Sell Stock

Say you have an array for which the ith element is the price of a given stock on day i. 
If you were only permitted to complete at most one transaction (ie, buy one and sell one share of the stock), design an algorithm to find the maximum profit.
Solution1:

public class Solution {
    public int maxProfit(int[] prices) {
        if (prices.length < 2)
            return 0;
        if (prices.length == 2)
            return prices[0] > prices[1] ? 0 : prices[1] - prices[0];
        
        int[] maxAfter = new int[prices.length-1];
        maxAfter[maxAfter.length-1] = prices[prices.length-1];
        
        for (int j = maxAfter.length - 2; j >= 0; j--)
            maxAfter[j] = maxAfter[j+1] > prices[j+1] ? maxAfter[j+1] : prices[j+1];

        int ans = 0;
        for (int i = 0; i < maxAfter.length; i++)
            ans = (maxAfter[i] - prices[i]) > ans ? (maxAfter[i] - prices[i]) : ans;
        return ans;
    }
}

Solution2: improved from solution1, space efficient

public class Solution {
    public int maxProfit(int[] prices) {
        if (prices.length < 2)
            return 0;
        
        int maxAfter = prices[prices.length-1];
        int maxProf = 0;
        
        for (int j = prices.length - 2; j >= 0; j--) {
            if (prices[j] < maxAfter) {
                int profit = maxAfter - prices[j];
            
                maxProf = profit > maxProf ? profit : maxProf;
            } 
            else 
                maxAfter = prices[j];
        }
        return maxProf;
    }
}