class Solution {
public:
    int maxDiff(vector<int>& nums) {
        if(nums.empty()) return 0;

        int res = 0;
        for(int i = 1,minv = nums[0];i < nums.size();++i){
            res = max(nums[i] - minv,res);
            minv = min(minv,nums[i]);
        }
        return res;
    }
};