LeetCode-in-Java

121. Best Time to Buy and Sell Stock

Easy

You are given an array prices where prices[i] is the price of a given stock on the ith 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 from this transaction. If you cannot achieve any profit, return 0.

Example 1:

Input: prices = [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. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell.

Example 2:

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

Output: 0

Explanation: In this case, no transactions are done and the max profit = 0.

Constraints:

To solve the “Best Time to Buy and Sell Stock” problem in Java with a Solution class, we’ll use a greedy algorithm. Below are the steps:

  1. Create a Solution class: Define a class named Solution to encapsulate our solution methods.

  2. Create a maxProfit method: This method takes an array prices as input and returns the maximum profit that can be achieved by buying and selling the stock.

  3. Initialize variables: Initialize two variables, minPrice to store the minimum price seen so far and maxProfit to store the maximum profit seen so far. Initialize maxProfit to 0.

  4. Iterate through the prices array:
    • For each price in the array:
      • Update minPrice to the minimum of the current price and minPrice.
      • Update maxProfit to the maximum of the current profit (price - minPrice) and maxProfit.
  5. Return the maximum profit: After iterating through the entire array, return maxProfit.

Here’s the Java implementation:

class Solution {
    public int maxProfit(int[] prices) {
        if (prices == null || prices.length <= 1) return 0; // Check for empty array or single element
        
        int minPrice = prices[0]; // Initialize minPrice to the first price
        int maxProfit = 0; // Initialize maxProfit to 0
        
        // Iterate through the prices array
        for (int i = 1; i < prices.length; i++) {
            minPrice = Math.min(minPrice, prices[i]); // Update minPrice
            maxProfit = Math.max(maxProfit, prices[i] - minPrice); // Update maxProfit
        }
        
        return maxProfit; // Return the maximum profit
    }
}

This implementation follows the steps outlined above and efficiently calculates the maximum profit that can be achieved by buying and selling the stock in Java.

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