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.

题意&解题思路：

将同样字母不同顺序的字符串聚集到一起。简单暴力，先对字母进行hash，再对该字符串的字母hash值再进行一次hash（hash2），若hash2已经存在，则表明之前已经有和当前字符串有相同字母其他形式的字符串出现了，直接加在这一类里，若hash2还不存在，则给该类分配一个新hash2值，再将该字符串分进该类。代码如下：

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;
    }
};