leetcode:49. Group Anagrams

Given an array of strings, group anagrams together.

For example, given: ["eat", "tea", "tan", "ate", "nat", "bat"], 
Return:

[
  ["ate", "eat","tea"],
  ["nat","tan"],
  ["bat"]
]

Note: All inputs will be in lower-case.

題意&解題思路：

將同樣字母不同順序的字符串聚集到一起。簡單暴力，先對字母進行hash，再對該字符串的字母hash值再進行一次hash（hash2），若hash2已經存在，則表明之前已經有和當前字符串有相同字母其他形式的字符串出現了，直接加在這一類裏，若hash2還不存在，則給該類分配一個新hash2值，再將該字符串分進該類。代碼如下：

class Solution {
public:
    vector<vector<string>> groupAnagrams(vector<string>& strs) {
        vector<vector<string>> ans;
        map<map<char, int>, int> ha;
        int num = strs.size();
        if(num == 0)return ans;
        vector<string>aa[num + 1];
        int ind = 1;
        for(int i = 0; i < num; i++){
            string s = strs[i];
            map<char, int>a;
            int len = s.length();
            for(int j = 0; j < len; j++){
                a[s[j]] += 1;
            }
            if(ha[a]){
                aa[ha[a]].push_back(s);
            }
            else {
                ha[a] = ind++;
                aa[ha[a]].push_back(s);
                
            }
        }
        for(int i = 1; i < ind; i++)ans.push_back(aa[i]);
        return ans;
    }
};