1427. Perform String Shifts

You are given a string s containing lowercase English letters, and a matrix shift, where shift[i] = [directioni, amounti]:

• directioni can be 0 (for left shift) or 1 (for right shift).
  amounti is the amount by which string s is to be shifted.
• A left shift by 1 means remove the first character of s and append it to the end.
• Similarly, a right shift by 1 means remove the last character of s and add it to the beginning.

Return the final string after all operations.

class Solution {
public:
    string stringShift(string s, vector<vector<int>>& shift) {
        int len = s.length(), mv = 0;
        for(auto shi : shift) {
            if(shi[0] == 0) mv -= shi[1];
            else mv += shi[1];
        }
        mv %= len;
        if(mv < 0) mv += len;
        
        return s.substr(len-mv) + s.substr(0, len - mv);
    }
};