Best Time to Buy and Sell Stock

Problem

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

You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock.

Return the maximum profit you can achieve. If no profit is possible, return 0.

Input / Output Format

Input: Array of prices prices. Output: Maximum achievable profit (integer).

Examples

Example 1

Input: prices = [7,1,5,3,6,4] Output: 5 Explanation: Buy on day 2 (price=1), sell on day 5 (price=6). Profit = 5.

Example 2

Input: prices = [7,6,4,3,1] Output: 0 Explanation: Prices only decrease — no profitable trade.

Approach Hints

• Single-Pass Tracking — Track minPriceSoFar while iterating left→right. At each day, profit = prices[i] - minPriceSoFar; update max profit. Time: O(n), Space: O(1).
• This is the simplest case of Kadane's algorithm: max subarray of daily price differences.
• Common pitfall: buying and selling on the same day — disallowed.