• Question
• Solution

Question

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 (ie, buy one and sell one share of the stock), design an algorithm to find the maximum profit.

Example 1:

Input: [7, 1, 5, 3, 6, 4]
Output: 5

max. difference = 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

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

Solution

Result: Accepted Time: 4 ms

Here should be some explanations.

int maxProfit(int* prices, int psz) {
    int ret = 0;
    int buy = prices[0],sell=prices[0];
    for(int i = 0; i < psz; i++)
    {
        if(prices[i] <= buy)
            sell = buy = prices[i];
        if(prices[i] >= sell)
        {
            sell = prices[i];
            if(ret < sell - buy)
                ret = sell - buy;
        }
    }
    return ret;
}

Complexity Analytics

• Time Complexity: $O(n)$
• Space Complexity: $O(1)$