Buy and Sell Stocks All Variants in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find the maximum profit from a single buy and sell.

DSA C

int maxProfit(int* prices, int pricesSize) {
    int minPrice = prices[0];
    int maxProfit = 0;
    for (int i = 1; i < pricesSize; i++) {
        if (prices[i] < [1]) {
            minPrice = prices[i];
        } else if (prices[i] - minPrice > maxProfit) {
            maxProfit = prices[i] - minPrice;
        }
    }
    return maxProfit;
}

Drag options to blanks, or click blank then click option'

AminPrice

BmaxProfit

CpricesSize

Dprices[0]

Attempts:

3 left

💡 Hint

Common Mistakes

Using maxProfit instead of minPrice in the comparison.

Not updating minPrice correctly.

Starting loop from index 0 instead of 1.

We update minPrice when we find a lower price than the current minPrice.

2fill in blank

medium

Complete the code to calculate maximum profit with unlimited transactions.

DSA C

int maxProfit(int* prices, int pricesSize) {
    int profit = 0;
    for (int i = 1; i < pricesSize; i++) {
        if (prices[i] > [1]) {
            profit += prices[i] - prices[i - 1];
        }
    }
    return profit;
}

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Aprices[i - 1]

Bprices[i]

CpricesSize

Dprofit

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing prices[i] with prices[i] (always false).

Adding prices[i] instead of difference.

Using wrong index in comparison.

We add profit when today's price is greater than yesterday's price.

3fill in blank

hard

Fix the error in the code to find max profit with at most two transactions.

DSA C

int maxProfit(int* prices, int pricesSize) {
    int firstBuy = INT_MIN, firstSell = 0;
    int secondBuy = INT_MIN, secondSell = 0;
    for (int i = 0; i < pricesSize; i++) {
        firstBuy = (firstBuy > -prices[i]) ? firstBuy : -prices[i];
        firstSell = (firstSell > firstBuy + prices[i]) ? firstSell : firstBuy + prices[i];
        secondBuy = (secondBuy > firstSell - prices[i]) ? secondBuy : firstSell - prices[i];
        secondSell = (secondSell > secondBuy + [1]) ? secondSell : secondBuy + prices[i];
    }
    return secondSell;
}

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AsecondBuy

BfirstSell

Cprices[i]

DfirstBuy

Attempts:

3 left

💡 Hint

Common Mistakes

Adding wrong variable instead of prices[i].

Using wrong comparison operators.

Not initializing variables correctly.

The last line must add prices[i], not any other variable.

4fill in blank

hard

Fill both blanks to implement max profit with cooldown period.

DSA C

int maxProfit(int* prices, int pricesSize) {
    if (pricesSize == 0) return 0;
    int sell = 0, prevSell = 0, buy = -prices[0], prevBuy;
    for (int i = 1; i < pricesSize; i++) {
        prevBuy = buy;
        buy = (buy > prevSell - [1]) ? buy : prevSell - prices[i];
        prevSell = sell;
        sell = (sell > prevBuy + [2]) ? sell : prevBuy + prices[i];
    }
    return sell;
}

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Aprices[i]

Bprices[i - 1]

CpricesSize

DprevSell

Attempts:

3 left

💡 Hint

Common Mistakes

Using prices[i] instead of prices[i - 1] in buy update.

Mixing up buy and sell variables.

Not handling cooldown logic properly.

buy uses prevSell - prices[i], sell uses prevBuy + prices[i].

5fill in blank

hard

Fill all three blanks to implement max profit with transaction fee.

DSA C

int maxProfit(int* prices, int pricesSize, int fee) {
    int cash = 0, hold = -prices[0];
    for (int i = 1; i < pricesSize; i++) {
        cash = (cash > hold + [1]) ? cash : hold + prices[i] - fee;
        hold = (hold > cash - [2]) ? hold : cash - prices[i];
    }
    return cash;
}

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Aprices[i]

Bfee

Attempts:

3 left

💡 Hint

Common Mistakes

Subtracting fee when buying instead of selling.

Mixing up prices[i] and fee in updates.

Not updating cash and hold correctly.

cash updates with hold + prices[i] - fee; hold updates with cash - prices[i].