Stock II - Implementation

Here is the solution:

function maxProfit(prices)
 profit := 0
 for i from 1 to length - 1
 if prices[i] > prices[i-1] then
 profit := profit + (prices[i] - prices[i-1])
 return profit

Time: $O(n)$. Space: $O(1)$.

Every positive difference means profit. If the price goes from $1$ to $5$, that is $4$ profit. If it then goes to $3$, you do not subtract (you already sold). If it goes from $3$ to $6$, that is $3$ more profit. Total: $7$.