Skip to main content

8. Best Time to Buy and Sell Stock

easyAsked at Flipkart

Find the max single-transaction profit from a price stream — Flipkart maps this to spotting the best discount window during a Big Billion Days sale event.

By Alex Chen, Founder, InterviewChamp.AI · Last verified

Problem

You are given an array prices where prices[i] is the price on the ith day. Choose one day to buy and a later day to sell to maximize profit. Return the maximum profit; 0 if no profit is possible.

Constraints

  • 1 <= prices.length <= 10^5
  • 0 <= prices[i] <= 10^4

Examples

Example 1

Input
prices = [7,1,5,3,6,4]
Output
5

Example 2

Input
prices = [7,6,4,3,1]
Output
0

Approaches

1. Brute force

Check every (buy, sell) pair.

Time
O(n^2)
Space
O(1)
for (let i=0;i<n;i++)
  for (let j=i+1;j<n;j++)
    best = Math.max(best, prices[j] - prices[i]);

Tradeoff:

2. Single pass min tracking

Track the minimum seen so far; for each day compute profit against that minimum and keep the best. One scan, O(1) memory.

Time
O(n)
Space
O(1)
function maxProfit(prices) {
  let min = Infinity, best = 0;
  for (const p of prices) {
    if (p < min) min = p;
    else if (p - min > best) best = p - min;
  }
  return best;
}

Tradeoff:

Flipkart-specific tips

Flipkart loves when you connect this to their sale-event price-tracking dashboards and discuss handling missing or out-of-order timestamps.

Solve it now

Free. No sign-up. Python and JavaScript run instantly in your browser.

Output

Press Run or Cmd+Enter to execute

Practice these live with InterviewChamp.AI

Drill Best Time to Buy and Sell Stock and other Flipkart interview questions under real-loop conditions with instant feedback on your reasoning, complexity claims, and code.

Practice these live with InterviewChamp.AI →