122. Best Time to Buy and Sell Stock II

At a Glance

Topic: arrays-hashing
Pattern: Greedy (accumulate positive daily deltas)
Difficulty: Medium
Companies: Amazon, Meta, Google, Microsoft, Bloomberg
Frequency: High
LeetCode: 122

Problem (one-liner)

Given prices for each day, you may complete as many buy–sell transactions as you like (must sell before buying again), but each day you hold at most one share. Return maximum total profit.

Recognition Cues

"Unlimited transactions", "may buy and sell same day multiple times conceptually"
Every upward step contributes — sum positive consecutive differences

Diagram

At-a-glance flow (replace with problem-specific Mermaid as you refine this note). camelCase node IDs; no spaces in IDs.

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Approaches

Brute force — enumerate transaction sequences — exponential.
Better — DP with states for hold/cash — O(n) time / O(n) space.
Optimal — greedy: add max(0, prices[day]-prices[day-1]) — O(n) time / O(1) space.

Optimal Solution

Go

package main

func maxProfit(prices []int) int {
	total := 0
	for dayIndex := 1; dayIndex < len(prices); dayIndex++ {
		delta := prices[dayIndex] - prices[dayIndex-1]
		if delta > 0 {
			total += delta
		}
	}
	return total
}

JavaScript

function maxProfit(prices) {
	let total = 0;
	for (let dayIndex = 1; dayIndex < prices.length; dayIndex++) {
		const delta = prices[dayIndex] - prices[dayIndex - 1];
		if (delta > 0) {
			total += delta;
		}
	}
	return total;
}