[leetcode] 249. Group Shifted Strings 解题报告

题目链接：https://leetcode.com/problems/group-shifted-strings/

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:

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

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

For example, given: ["abc", "bcd", "acef", "xyz", "az", "ba", "a", "z"], 
Return:

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

Note: For the return value, each inner list's elements must follow the lexicographic order.

思路：将每个字符串都转换成减去字符串首字符之后的字符串，这样可以相互转换的字符串就转化成了一个key，然后用map将以这个key保存所有可以相互转换字符串的集合．

代码如下：

class Solution {
public:
    vector<vector<string>> groupStrings(vector<string>& strings) {
        unordered_map<string, vector<string>> mp;
        vector<vector<string>> result;
        for(auto str: strings)
        {
            string tem = str;
            for(int i =tem.size()-1; i >=0; i--)
                tem[i] = ('a'+(tem[i]-tem[0]+26)%26);
            mp[tem].push_back(str);
        }
        for(auto val: mp)
        {
            sort(val.second.begin(), val.second.end());
            result.push_back(val.second);
        }
        return result;
    }
};