DSA TrainerBest Time to Buy and Sell Stock II
Given an array of stock prices where prices[i] is the price on day i, you can buy and sell on any day (but must sell before buying again). Return the maximum total profit.
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Problem
You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day, you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. Find and return the maximum profit you can achieve.
Input
An integer array `prices`.
Output
The maximum profit you can achieve.
Examples
Input: prices = [7,1,5,3,6,4]
Output: 7
Buy day 2 (price=1), sell day 3 (price=5), profit=4. Buy day 4 (price=3), sell day 5 (price=6), profit=3. Total=7.
Input: prices = [1,2,3,4,5]
Output: 4
Buy day 1, sell day 5. Or equivalently, add up each consecutive positive difference.
The brute-force approach
Try all combinations of buy/sell days. Track the maximum profit.
# Exponential — not practical.Exponential number of trading sequences.
Spotting the pattern
This is a Greedy problem. The key question to ask yourself:
Why does summing all positive consecutive differences give the same result as finding the optimal set of buy/sell transactions?
Answering that is where it clicks, and it's exactly what the guided walkthrough below builds with you: the pattern reasoning, a progressive hint ladder that never spoils the answer, a row-by-row dry run, the optimized solution, and an in-browser editor to run your code against real test cases.
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