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 from this transaction. If you cannot achieve any profit, return 0.
Example 1
Input: prices = [7,1,5,3,6,4]
Output: 5
Explanation: Buy on day 2 (price=1), sell on day 5 (price=6), profit=5.
Example 2
Input: prices = [7,6,4,3,1]
Output: 0
Explanation: No transaction gives profit.
1 <= prices.length <= 10^50 <= prices[i] <= 10^4The brute force checks every (buy day, sell day) pair directly — O(n^2).
You never need to remember every past price — only the LOWEST price seen so far, since that's always the best possible buy day up to this point.
At each day, ask: if I sold TODAY, having bought at the lowest price seen SO FAR, what's my profit? Track the best such profit across all days.
public int maxProfitBruteForce(int[] prices) {
int maxProfit = 0;
for (int i = 0; i < prices.length; i++) {
for (int j = i + 1; j < prices.length; j++) {
maxProfit = Math.max(maxProfit, prices[j] - prices[i]);
}
}
return maxProfit;
}Time: O(n^2) · Space: O(1)