You are given an array `prices` where `prices[i]` represents the price of a stock on day `i`.

Your goal is to find the maximum profit you can make by:
1. Buying the stock on exactly **one day**
2. Selling the stock on a **different day in the future** (after the buy day)

You need to return the maximum profit possible from this single buy-sell transaction. If no profit can be made (for example, if prices only decrease), return `0`.

**Key constraints:**
- You must buy before you sell (the sell day must come after the buy day)
- You can only make one transaction (one buy and one sell)
- You cannot buy and sell on the same day

**Example scenarios:**
- If `prices = [7, 1, 5, 3, 6, 4]`, the maximum profit would be `5` (buy at price `1` on day 2, sell at price `6` on day 5)
- If `prices = [7, 6, 4, 3, 1]`, the maximum profit would be `0` (prices keep decreasing, so no profit is possible)

The solution maintains a running minimum price (`mi`) as it iterates through the array, and for each price, calculates the potential profit if selling at that price. The variable `ans` keeps track of the maximum profit found so far. The algorithm efficiently finds the best buy-sell pair in a single pass through the array with `O(n)` time complexity.


121. Best Time to Buy and Sell Stock

Given an array `prices` where `prices[i]` is the price of a given stock on day `i`, find the maximum profit you can achieve. You may only complete one transaction (i.e., buy one and sell one share of the stock).

Sliding Window Flexible - Longest

Best Time to Buy and Sell Stock

Two Sum

Contains Duplicate

Group Anagrams

Top K Frequent Elements

Longest Consecutive Sequence

Valid Palindrome

Container With Most Water

3Sum

Trapping Rain Water

Longest Substring Without Repeating Characters

Longest Repeating Character Replacement

Minimum Window Substring

Valid Parentheses

Min Stack

Daily Temperatures

Binary Search

Find Minimum in Rotated Sorted Array

Search in Rotated Sorted Array

Reverse Linked List

Merge Two Sorted Lists

Linked List Cycle

Remove Nth Node From End of List

Merge Intervals

Insert Interval

Non-overlapping Intervals

Same Tree

Maximum Depth of Binary Tree

Invert Binary Tree

Binary Tree Level Order Traversal

Validate Binary Search Tree

Kth Smallest Element in a BST

Lowest Common Ancestor of a Binary Tree

Number of Islands

Clone Graph

Graph Valid Tree

Course Schedule

Pacific Atlantic Water Flow

Word Ladder

K Closest Points to Origin

Merge K Sorted Lists

Find Median from Data Stream

Combination Sum

Word Search

N-Queens

Climbing Stairs

House Robber

Coin Change

Word Break

Longest Increasing Subsequence

Longest Palindromic Substring

Palindromic Substrings

Missing Number

Reorder List

Alien Dictionary

Encode and Decode Strings

Maximum Product Subarray

Serialize and Deserialize Binary Tree

Rotate Image

Maximum Subarray

Spiral Matrix

Jump Game

Subtree of Another Tree

Unique Paths

Reverse Bits

Number of 1 Bits

Number of Connected Components in an Undirected Graph

Set Matrix Zeroes

Implement Trie (Prefix Tree)

Counting Bits

Word Search II

House Robber II

Decode Ways

Meeting Rooms II

Longest Common Subsequence

Construct Binary Tree from Preorder and Inorder Traversal

Product of Array Except Self

Sum of Two Integers

Meeting Rooms

Binary Tree Maximum Path Sum

Example:

Test Cases

Example:

Test Cases

Study Notes

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