Stock Buy and Sell – Max one Transaction Allowed

JavaView on GFG

Time: O(n)

Space: O(1)

Intuition

Track minimum price seen so far. At each day, profit = price - min_so_far. Track maximum profit.

Algorithm

1min_price = prices[0], max_profit = 0.
2For each price: max_profit = max(max_profit, price - min_price). min_price = min(min_price, price).

Common Pitfalls

•Must buy before selling. Update min_price at the end (or in same step since profit uses current price).

Stock Buy and Sell – Max one Transaction Allowed.java

Java

// Approach: Track minimum price seen so far; at each day, max profit = price - minPrice. Update max profit.
// Time: O(n) Space: O(1)
class Solution {
    public int maximumProfit(int prices[]) {
        int minSofar = prices[0];
        int maxDiff = 0;

        for (int i = 1; i < prices.length; i++) {
            if (prices[i] < minSofar) {
                minSofar = prices[i];
            }

            maxDiff = Math.max(maxDiff, prices[i] - minSofar);
        }

        return maxDiff;
    }
}

class Solution1 {
    public int maxProfit(int[] prices) {
        int n = prices.length;
        int minPrice = prices[0];
        int maxProfit = 0;

        for (int i = 1; i < n; i++) {
            minPrice = Math.min(prices[i], minPrice);
            int profit = prices[i] - minPrice;
            maxProfit = Math.max(profit, maxProfit);
        }
        return maxProfit;
    }
}

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