【LeetCode】49. Group Anagrams 解題報告

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49. Group Anagrams / Medium

Given an array of strings strs, group the anagrams together. You can return the answer in any order.

An Anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once.

Example 1:

Input: strs = [“eat”,”tea”,”tan”,”ate”,”nat”,”bat”]
Output: [[“bat”],[“nat”,”tan”],[“ate”,”eat”,”tea”]]

Example 2:

Input: strs = [“”]
Output: [[“”]]

Example 3:

Input: strs = [“a”]
Output: [[“a”]]

Constraints:

  • 1 <= strs.length <= 10^4
  • 0 <= strs[i].length <= 100
  • strs[i] consists of lower-case English letters.

Solution: Map

思路

開一個 map，key 是排序後的字串，value 是該字串在 vector 中對應的 index。
把每個字串排序後放進 map 查 index，再把沒排序過的 string 放到對應的 vector。

效能

Complexity

  • Time Complexity: O(K*NlogN) where N is the length of string and K is number of strings.
  • Space Complexity: O(N)

LeetCode Result

Code

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class Solution {
public:
    vector<vector<string>> groupAnagrams(vector<string>& strs) {
        unordered_map<string, int> umap;
        vector<vector<string>> ans;
        int count = 0;
        for(const auto& str: strs) {
            string tmp(str);
            sort(tmp.begin(), tmp.end());
            if(umap.count(tmp) <= 0) {
                umap[tmp] = count;
                ++count;
                ans.emplace_back(vector<string>(0));
            } 
            ans[umap[tmp]].emplace_back(str);
        }
        return ans;
    }
};