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Group Shifted Strings

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Description

Given a string, we can “shift” each of its letter to its successive letter, for example: "abc" -> "bcd". We can keep “shifting” which forms the sequence:

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"abc" -> "bcd" -> ... -> "xyz"

Given a list of strings which contains only lowercase alphabets, group all strings that belong to the same shifting sequence.

Example:

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Input: ["abc", "bcd", "acef", "xyz", "az", "ba", "a", "z"],
Output: 
[
  ["abc","bcd","xyz"],
  ["az","ba"],
  ["acef"],
  ["a","z"]
]

Solution

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class Solution {
public:
    vector<vector<string>> groupStrings(vector<string>& strings) {
        unordered_map<int, vector<string>> mapping;
        for(auto& item : strings) {
            int hashValue = 0;
            int base = 1;
            for (int i = 1; i < item.size(); ++i){
                hashValue += base * distance(item[i-1], item[i]);
                base *= 26;
            }
            mapping[hashValue].push_back(item);
        }
        
        vector<vector<string>> ret;
        for(auto& item : mapping) {
            ret.push_back(item.second);
        }
        
        return ret;
    }
    
    int distance(char a, char b) {
        return b - a + (a < b ? 0 : 26);
    }
};