Best Time to Buy and Sell Stock

LeetCode#121. Best Time to Buy and Sell Stock

Problem Statement

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

Golang Solution

func maxProfit(prices []int) int {
    start := 0
    maxProfit := 0

    if len(prices) > (10*10*10*10*10){
        return 0
    }

    for i:=1; i < len(prices); i++ {
        if prices[i] > (10*10*10*10){
            return 0
        }
        if prices[start] > prices[i]{
            start = i
        }else if maxProfit < (prices[i]-prices[start]){
            maxProfit = prices[i]-prices[start]
        }
    }
    return maxProfit
}

Time Complexity

• O(n) since we are iterating through the array once.

Space Complexity

• O(1) since we only use a few variables to track the maxprofit .

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