[LeetCode] 893. Groups of Special-Equivalent Strings 特殊字符串的群組

You are given an array `A` of strings.

Two strings S and T are special-equivalent if after any number of moves, S == T.

A move consists of choosing two indices i and jwith i % 2 == j % 2, and swapping S[i] with S[j].

Now, a group of special-equivalent strings from A is a non-empty subset S of A such that any string not in S is not special-equivalent with any string in S.

Return the number of groups of special-equivalent strings from A.

Example 1:

Input: ["a","b","c","a","c","c"]
Output: 3
Explanation: 3 groups ["a","a"], ["b"], ["c","c","c"]

Example 2:

Input: ["aa","bb","ab","ba"]
Output: 4
Explanation: 4 groups ["aa"], ["bb"], ["ab"], ["ba"]

Example 3:

Input: ["abc","acb","bac","bca","cab","cba"]
Output: 3
Explanation: 3 groups ["abc","cba"], ["acb","bca"], ["bac","cab"]

Example 4:

Input: ["abcd","cdab","adcb","cbad"]
Output: 1
Explanation: 1 group ["abcd","cdab","adcb","cbad"]

Note:

• 1 <= A.length <= 1000
• 1 <= A[i].length <= 20
• All A[i] have the same length.
• All A[i] consist of only lowercase letters.

這道題定義了一種特殊相等的關系，就是說對於一個字符串，假如其偶數位字符之間可以互相交換，且其奇數位字符之間可以互相交換，交換后若能跟另一個字符串相等，則這兩個字符串是特殊相等的關系。現在給了我們一個字符串數組，將所有特殊相等的字符串放到一個群組中，問最終能有幾個不同的群組。最開始的時候博主沒仔細審題，以為是隨意交換字母，就直接對每個單詞進行排序，然后扔到一個 HashSet 中就行了。后來發現只能是奇偶位上互相交換，於是只能現先將奇偶位上的字母分別抽離出來，然后再進行分別排序，之后再合並起來組成一個新的字符串，再丟到 HashSet 中即可，利用 HashSet 的自動去重復功能，這樣最終留下來的就是不同的群組了，參見代碼如下：

class Solution {
public:
    int numSpecialEquivGroups(vector<string>& A) {
        unordered_set<string> st;
        for (string word : A) {
            string even, odd;
            for (int i = 0; i < word.size(); ++i) {
                if (i % 2 == 0) even += word[i];
                else odd += word[i];
            }
            sort(even.begin(), even.end());
            sort(odd.begin(), odd.end());
            st.insert(even + odd);
        }
        return st.size();
    }
};

Github 同步地址:

https://github.com/grandyang/leetcode/issues/893

參考資料：

https://leetcode.com/problems/groups-of-special-equivalent-strings/

https://leetcode.com/problems/groups-of-special-equivalent-strings/discuss/163413/Java-Concise-Set-Solution

https://leetcode.com/problems/groups-of-special-equivalent-strings/discuss/163412/C%2B%2B-Simple-Solution

https://leetcode.com/problems/groups-of-special-equivalent-strings/discuss/163891/C%2B%2B-Create-a-signature-for-each-string

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