tianlipa

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int ans = 0;
        int sell = -1;
        for(int i = prices.size() - 1; i >= 0; --i) {
            ans = max(ans, sell - prices[i]);
            sell = max(sell, prices[i]);
        }
        return ans;
    }
};

class Solution {
public:
    bool isPalindrome(string s) {
        int left = 0, right = s.size() - 1;
        for(int i = 0; i < s.size(); ++i) {
            if(s[i] <= 'Z' && s[i] >= 'A') {
                s[i] = s[i] + 'a' - 'A';
            }
        }
        // cout<<s;
        while(left <= right) {
            if(!(s[left] <= 'z' and s[left] >='a') and !(s[left] <= '9' and s[left] >= '0')) {
                ++left;
                continue;
            }
            if(!(s[right] <= 'z' and s[right] >='a') and !(s[right] <= '9' and s[right] >= '0')) {
                --right;
                continue;
            }
            if(s[left++] != s[right--])
                return false;
        }
        return true;
    }
};