股票的最大利润

class Solution {
public:
    int maxDiff(vector<int>& nums) {
        if(nums.size()==0)  return 0;
        int buy=nums[0],res=0;
        for (int i = 1; i < nums.size(); i ++ )
        {
            res=max(res,nums[i]-buy);
            buy=min(buy,nums[i]);
        }
        return res;
    }
};