买卖股票最好时机

记录一下最小值，O(N)扫一遍

class Solution {
public:
    /**
     * 
     * @param prices int整型vector 
     * @return int整型
     */
    int maxProfit(vector<int>& prices) {
        int minn = 0x3f3f3f3f,ans = 0;
        for(auto i:prices)
        {
            ans = max(ans,i - minn);
            minn = min(i,minn);
        }
        return ans;
    }
};