Best Time to Buy and Sell Stock in Java

The challenge

Say you have an array for which the i^th element is the price of a given stock on day i.

If you were only permitted to complete at most one transaction (i.e., buy one and sell one share of the stock), design an algorithm to find the maximum profit.

Note that you cannot sell a stock before you buy one.

Example 1:

Input: [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.
             Not 7-1 = 6, as selling price needs to be larger than buying price.

Example 2:

Input: [7,6,4,3,1]
Output: 0
Explanation: In this case, no transaction is done, i.e. max profit = 0.

The solution in Java

class Solution {
    public int maxProfit(int[] prices) {
        // create a profit variable to return
        int maxprofit = 0;
        
        // loop through the original array
        for (int i=0; i<prices.length-1; i++) {
            // loop through the array from the next item on
            for (int j=i+1; j<prices.length; j++) {
                // if in bounds and next is greater than current
                if (j<prices.length && prices[j]>prices[i]) {
                    // work out profit
                    int tmp = prices[j]-prices[i];
                    // report the profit
                    if (tmp>maxprofit) maxprofit = tmp;
                }
            }
        }
        
        // return out profit
        return maxprofit;
    }
}
Code language: Java (java)