[Leetcode] Best Time to Buy and Sell Stock

class Solution {
public:
    int maxProfit(vector<int> &a) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int minIdx = 0;
        int diff = 0;
        int res = 0;
        
        for (int i = 1; i < a.size(); ++i)
        {
            if (a[minIdx] > a[i])
                minIdx = i;
            
            if (a[i] - a[minIdx] > res)
            {
                res = a[i] - a[minIdx];
                
            }
        }
        
        return res;
    }
};