Skip to main content

4. Best Time to Buy and Sell Stock

easyAsked at JetBrains

Find the max profit from one buy and one sell over a price array — a single-pass scan that mirrors the streaming token analyses inside JetBrains lexers.

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

Problem

Given an array prices where prices[i] is the price of a stock on day i, return the maximum profit you can achieve from buying once and selling later. If no profit is possible, return 0.

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 pairs

Try every buy/sell pair; quadratic.

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

Tradeoff:

2. Single-pass min-tracking

Track running minimum buy and best profit in one scan. Same single-pass discipline as a JetBrains lexer accumulating state token by token.

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:

JetBrains-specific tips

JetBrains expects you to highlight the constant-space streaming property — they value single-pass analyses that fit into incremental parsing budgets.

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

Practice these live with InterviewChamp.AI →