Best Time to Buy and Sell Stock II

class Solution {
public:
    int solve(int index, int buy, vector<int>& prices, vector<vector<int>>& dp){
        if(index == prices.size()){
            return 0;
        }
        if(dp[index][buy] != -1){
            return dp[index][buy];
        }
        int profit = 0;
        if(buy){
            profit = max((-prices[index] + solve(index+1, 0, prices, dp)), (0 + solve(index + 1, 1, prices, dp)));
        } 
        else{
            profit = max((prices[index] + solve(index+1, 1, prices, dp)), (0 + solve(index + 1, 0, prices, dp)));
        }
        return dp[index][buy] = profit;
    }

    int solveTab(vector<int>& prices){ 
        vector<vector<int>> dp(prices.size()+1, vector<int>(2, 0));
        for(int index = prices.size()-1; index >= 0; index--){
            for(int buy = 0; buy <= 1; buy++){
                int profit = 0;
                if(buy){
                    profit = max((-prices[index] + dp[index+1][0]), (0 + dp[index+1][1]));
                } 
                else{
                    profit = max((prices[index] + dp[index+1][1]), (0 + dp[index+1][0]));
                }
                dp[index][buy] = profit;
            }
        }
        return dp[0][1];
    }

    int solveSpace(vector<int>& prices){
        vector<int> curr(2, 0);
        vector<int> next(2, 0);

        for(int index = prices.size()-1; index >= 0; index--){
            for(int buy = 0; buy <= 1; buy++){
                int profit = 0;
                if(buy){
                    profit = max((-prices[index] + next[0]), (0 + next[1]));
                } 
                else{
                    profit = max((prices[index] + next[1]), (0 + next[0]));
                }
                curr[buy] = profit;
            }
            next = curr;
        }
        return curr[1];

    }
    int maxProfit(vector<int>& prices) {
        // vector<vector<int>> dp (prices.size(), vector<int>(2, -1));
        // return solve(0, 1, prices, dp);
    
        // return solveTab(prices);

        return solveSpace(prices);
    }
};