1. Problem Statement

You are given an array prices[] where prices[i] is the stock price on the i-th day.

You may:

• Buy and/or sell the stock any number of times.
• You can buy and sell on the same day.
• You cannot hold more than one share at a time.

Goal: Return the maximum profit you can make.

Example:

Input:
prices = [7,1,5,3,6,4]

Output:
7

Explanation:

• Buy on day 1 (price = 1), sell on day 2 (price = 5) → profit = 4
• Buy on day 3 (price = 3), sell on day 4 (price = 6) → profit = 3
• Total profit = 4 + 3 = 7

2. Solution approach

Let’s look at this example:

prices = [7, 1, 5, 3, 6, 4]

We represent each day and compare it with the previous one:

Day:       0   1   2   3   4   5
Price:     7   1   5   3   6   4
Change:        ↓   ↑   ↓   ↑   ↓
             (↓) (profit) (↓) (profit)

Profit Calculation:

• Day 1: Price = 1 (lower than 7) → No profit
• Day 2: Price = 5 (higher than 1) → Buy at 1, Sell at 5 → Profit = 4
• Day 3: Price = 3 (lower than 5) → No profit
• Day 4: Price = 6 (higher than 3) → Buy at 3, Sell at 6 → Profit = 3
• Day 5: Price = 4 (lower than 6) → No profit

Total Profit = 4 + 3 = 7

3. Approach in Simple Words

• Start from day 1 and move through the array.
• If today’s price is more than yesterday’s, we assume:
  • We bought the stock yesterday
  • Sold it today
  • Add the profit to our total
• Do this for every upward price move.

Let’s simulate it step by step:

prices = [7, 1, 5, 3, 6, 4]
profit = 0

Day 1: 1 < 7 → no action
Day 2: 5 > 1 → profit += 5 - 1 = 4
Day 3: 3 < 5 → no action
Day 4: 6 > 3 → profit += 6 - 3 = 3
Day 5: 4 < 6 → no action

Total profit = 4 + 3 = 7

4. Java implementation

public class StockProfitCalculator {
    public int maxProfit(int[] prices) {
        int profit = 0;

        for (int i = 1; i < prices.length; i++) {
            if (prices[i] > prices[i - 1]) {
                profit += prices[i] - prices[i - 1];
            }
        }

        return profit;
    }
}