121. Best Time to Buy and Sell Stock

Description

Say you have an array for which the ith element is the price of a given stock on day i.

If you were only permitted to complete at most one transaction (i.e., buy one and sell one share of the stock), design an algorithm to find the maximum profit.

Note that you cannot sell a stock before you buy one.

Constraints

Approach

Links

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

Example 1

Input: [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. Not 7-1 = 6, as selling price needs to be larger than buying price.

Example 2

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

Output: 0

Explanation: In this case, no transaction is done, i.e. max profit = 0.

Solutions

Solution 1

/**
 * Time complexity : O(N)
 * Space complexity : O(1)
 */

class Solution {
    public int maxProfit(int[] prices) {
        
        if(prices == null || prices.length < 2) return 0;
        
        int maxProfit = 0;
        int minStockSoFar = prices[0];
        
        for(int i = 1; i < prices.length; i++) {
            minStockSoFar = Math.min(minStockSoFar, prices[i]);
            maxProfit = Math.max(maxProfit, prices[i]-minStockSoFar);
        }
        
        return maxProfit;
    }
}

Follow up