121. Best Time to Buy and Sell Stock

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int n=prices.size();
      int b=prices[0];
      int s=0, ans=0, max=0; 
    for(int i=1; i<n; i++)
    {
        if(prices[i]<b)
        {
           if(max<s-b)
              max=s-b;
           b=prices[i];
           ans=0;
        }
        else if(s<prices[i]){
            s=prices[i];
            ans=1;
           // max=s-b;
        }
        if(ans==0)
        { 
          s=0;
        }
        
    }
    if(s>b || max>0)
    {
        if((s-b)>max)
           return s-b;
        else
           return max;
    }
    else 
        return 0;
    }
};