121. Best Time to Buy and Sell Stock.java

/*
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:

1 <= prices.length <= 105
0 <= prices[i] <= 104
*/


//Solution:
class Solution {
    public int maxProfit(int[] prices) {
        if(prices.length == 0 ){
            return 0;
        }
        int profit = 0;
        int buy = prices[0];
        for(int j = 1;j < prices.length;j++){
            if(prices[j] > buy){
                if(profit < prices[j] - buy)
                    profit = prices[j] - buy;
            }else{
                buy = prices[j];
            }
        }   
        
        return profit;
    }
}