Best Time to Buy and Sell Stock @leetcode

Plan A:

int maxProfit(vector<int> &prices) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        int i;
        int res=0;
        if(prices.size() == 0 || prices.size()==1)
        {
            return 0;
        }
        vector<int> highestAfterThis;
        highestAfterThis.resize(prices.size()-1);
        for(i=highestAfterThis.size()-1;i>=0;--i)
        {
            if(i == highestAfterThis.size() -1)
                highestAfterThis[i] = prices[prices.size()-1];
            else
            {
                highestAfterThis[i] = prices[i+1]>highestAfterThis[i+1]?prices[i+1]:highestAfterThis[i+1];
            }
        }
        for(i=0;i<prices.size()-1;++i)
        {
            int tmp = highestAfterThis[i] - prices[i];
            if(tmp > res )res = tmp;
        }
        return res;
    }

Plan B:

int maxProfit(vector<int> &prices) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        int i;
        int res=0;
        if(prices.size() == 0 || prices.size()==1)
        {
            return 0;
        }
        int min=prices[0];
        for(i=0;i<prices.size();++i)
        {
            if(prices[i] < min) min = prices[i];
            if(prices[i] - min > res) res = prices[i] - min;
        }
        return res;
    }