best time to buy sell stock

http://www.lintcode.com/en/problem/best-time-to-buy-and-sell-stock/

code 2

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int n = prices.size();
        if(n == 0)
        {
            return 0;
        }

        int lowest_price = INT_MAX;
        int profit = 0;

        for(int price : prices)
        {
            lowest_price = min(lowest_price, price);
            profit = max(profit, price-lowest_price);
        }

        return profit;
    }
};

code

class Solution {
public:
    /**
     * @param prices: Given an integer array
     * @return: Maximum profit
     */
    int maxProfit(vector<int> &prices) {
        // write your code here
        if(prices.size() == 0)
        {
            return 0;
        }

        vector<int> shadow;
        for(int i = 1; i<prices.size(); i++)
        {
            shadow.push_back(prices[i] - prices[i-1]);
        }

        int sum = 0;
        int minsum = 0;
        int ret = 0;

        for(int i = 0; i<shadow.size(); i++)
        {
            sum += shadow[i];
            ret = max(ret, sum-minsum);
            minsum = min(minsum, sum);
        }

        return ret;
    }
};