Skip to main content

5. Best Time to Buy and Sell Stock

easyAsked at Byju's

Maximize profit from one buy and one sell across an array of daily prices.

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

Problem

You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve, or 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)
let max=0;
for(let i=0;i<prices.length;i++)
  for(let j=i+1;j<prices.length;j++)
    max=Math.max(max,prices[j]-prices[i]);
return max;

Tradeoff:

2. Single-pass min tracking

Track the minimum price so far and the best profit at each step. One linear scan finishes the job.

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

Tradeoff:

Byju's-specific tips

Byju's leans on adaptive-learning analogies, so framing min-tracking as a 'best progress so far' student-score recommendation lands well with interviewers.

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 Byju's interview questions under real-loop conditions with instant feedback on your reasoning, complexity claims, and code.

Practice these live with InterviewChamp.AI →