Given an array of strings, group anagrams together.
For example, given: ["eat", "tea", "tan", "ate", "nat", "bat"],
Return:
[ ["ate", "eat","tea"], ["nat","tan"], ["bat"]]
使用一个Map里面的键是经过排序的字符串，值是这类字符串在结果数组中的位置。

var groupAnagrams = function(strs) {
    var num = strs.length;
    var map = {};
    var res = [];
    var index = 0;
    for(var i = 0;i < num;i++) {
        var temp = strs[i].split("");      
        temp.sort();             
        temp = temp.join("");   
        if (map[temp]===undefined) {
            map[temp] = index;
            res.push([]);
            res[index].push(strs[i]);
            index++;
        } else {
            res[map[temp]].push(strs[i]);
        }
    }
    return res;
};