买股票的最佳时机

class Solution {
public:
    /**
     * @param prices: Given an integer array
     * @return: Maximum profit
     */
    int maxProfit(vector<int> &prices) {
        // write your code here
        int n = prices.size();
        if (n <= 1) return 0;
        vector<int> trans;
        for (int i = 1; i <= n; i++)
            trans.push_back(prices[i] - prices[i-1]);
        int imax = 0, res = 0;
        for(int i = 0; i < n-1; i++){
            imax += trans[i];
            if (imax > res) res = imax;
            else if(imax < 0) imax = 0;
        }
        return res;
    }
};