Best Time to Buy and Sell Stock

Question

You are given an array prices where prices[i] is the price of a stock on day i. You want to buy one share and sell it later. Return the maximum profit you can get.

If no profit can be made, return 0.

Example

Input: prices = [7, 2, 3, 4, 9, 1]

Output: 7

Explanation: Buy on day 1 (price = 1) and sell on day 4 (price = 9), profit = 9 - 2 = 7.

My Notes

Keep track of the minimum price seen so far while looping.
On each day, check if selling today (current price - min price) gives a better profit.
Update the maximum profit if it's better than previous value.
🔁 One pass, constant space.
🧠 Intuition: Track lowest valley (buy) and highest peak (sell after it).

package main

import (
    "fmt"
)

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

    for _, price := range prices[1:] {
        if price < minPrice {
            minPrice = price
            continue
        }

        if price-minPrice > maxProfit {
            maxProfit = price - minPrice
        }
    }

    return maxProfit
}

func main() {
    result := maxProfit([]int{7, 2, 3, 4, 9, 1})
    fmt.Println(result)
}