Character , Array and Strings Questions

//Count SUbstrings

class Solution {
public:
    int expandAroundIndex(string s, int left, int right) {
        int count = 0;
        //jab tak match karega, tab tak count increment kardo and i piche and j aaage kardo
        while(left >= 0 && right <s.length() && s[left] == s[right] ) {
            count++;
            left--;
            right++;
        }
        return count;
    }

    int countSubstrings(string s) {
        int totalCount = 0;
        int n = s.length();

        for(int center=0; center<n; center++) {
            //odd
            int oddKaAns = expandAroundIndex(s, center, center);
            totalCount = totalCount + oddKaAns;
            //even
            int evenKaAns = expandAroundIndex(s,center,center+1);
            totalCount = totalCount + evenKaAns;
        }

        return totalCount;
    }
};

//Find Minimum Distance
class Solution {
public:
    int findMinDifference(vector<string>& timePoints) {
        //step1: convert time string into minutes integer value
        vector<int> minutes;

        for(int i=0; i<timePoints.size(); i++) {
            string curr = timePoints[i];

            int hours = stoi( curr.substr(0,2) );
            int min = stoi( curr.substr(3,2) );
            int totalMinutes = hours*60 + min;
            minutes.push_back(totalMinutes);
        }

        //Step2: sort
        sort(minutes.begin(), minutes.end());

        //Step3: difference and calculate min diff
        int mini = INT_MAX;
        int n = minutes.size();

        for(int i=0; i<n-1; i++) {
            int diff = minutes[i+1] - minutes[i];
            mini = min(mini, diff);
        }

        //something missing - THIS IS THE GAME
        int lastDiff1 = (minutes[0] + 1440) - minutes[n-1];
        int lastDiff2 = minutes[n-1] - minutes[0];
        int lastDiff = min(lastDiff1, lastDiff2);
        mini = min(mini, lastDiff);

        return mini;

    }
};

//Remove Duplicate Strings
class Solution {
public:
    string removeDuplicates(string s) {
        string ans ="";
        int i = 0;

        while( i < s.length() ) {

                if( ans.length() > 0  &&  ans[ans.length() - 1] == s[i]) {
                    ans.pop_back();
                }
                else {
                    ans.push_back(s[i]);
                }
            i++;
        }
        return ans;
    }
};


//Remove Occurences

class Solution {
public:
    string removeOccurrences(string s, string part) {
        int pos = s.find(part);
        while(pos != string::npos) {
            s.erase(pos, part.length());
            pos = s.find(part);
        }
        return s;
    }
};

//Valid Palindrome

class Solution {
public:
    bool checkPalindrome(string s, int i, int j ) {
        while(i <= j) {
            if(s[i] != s[j] )
                return false;
            i++;
            j--;
        }
        return true;
    }
    bool validPalindrome(string s) {
        int i = 0;
        int j = s.length() - 1;

        while(i<=j) {
            if(s[i] != s[j]) {
                //ek baar i ko remove, ek baar j ko remove
                return checkPalindrome(s,i+1, j) || checkPalindrome(s, i, j-1);
            }
            else {
                //s[i] == s[j]
                i++;
                j--;
            }
        }
        return true;
    }
};