Rotation Groups - Amazon Top Interview Questions

Problem Statement :

A rotation group for a string contains all of its unique rotations. For example, "123" can be rotated to "231" and "312" and they are all in the same rotation group.

Given a list of strings words, group each word by their rotation group, and return the total number of groups.


n ≤ 200 where n is the length of words.

Example 1


words = ["abc", "xy", "yx", "z", "bca"]




There are three rotation groups:

["abc", "bca"]
["xy", "yx"]

Solution :


                        Solution in C++ :

int solve(vector<string>& words) {
    unordered_set<string> vis;

    for (string& s : words) {
        for (int i = 0; i < s.size(); i++) {
            rotate(s.begin(), s.begin() + 1, s.end());
            if (vis.count(s)) break;

    return vis.size();

                        Solution in Java :

import java.util.*;

class Solution {
    public int solve(String[] words) {
        ArrayList<String> set = new ArrayList<>();
        for (String word : words) {
            boolean exist = false;
            for (String rotation : set) {
                if (rotation.length() == word.length() * 2 && rotation.contains(word)) {
                    exist = true;
            if (!exist) {
                set.add(word + word);
        return set.size();

                        Solution in Python : 
class Solution:
    def solve(self, words):
        s = set()
        for ind in range(len(words)):
            c = words[ind]

            for i in s:
                if len(c) == len(i) and c in i * 2:
        return len(s)

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