49. Group Anagrams [Medium]

49. Group Anagrams

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.

Constraints:

• 1 <= strs.length <= 104
• 0 <= strs[i].length <= 100
• strs[i] consists of lowercase English letters.

Example

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

思路

做这题前先去做217. Contains Duplicate [Easy]，有了这题的基础后，很自然就能联想到这些Anagrams他们经过排序后，一定会相同，拿这个作为他们的key来区分就行了

题解

    public List<List<String>> groupAnagrams(String[] strs) {
	// key就是经过排序后的anagram，value就来存结果
        HashMap<String, List<String>> result = new HashMap<>();
        for (String val : strs) {
            char[] keyChar = val.toCharArray();
            Arrays.sort(keyChar);
	    // 拿到经过排序后的key
            String key = String.valueOf(keyChar);
	   // 去Map里找有没有这个key，没有的话他就是第一个，new一个List，把它放进去
            if (!result.containsKey(key))
                result.put(key, new ArrayList<>(Arrays.asList(val)));
            else {
	   // 有的话就往里面塞
                result.get(key).add(val);
            }
        }
	  // 转换成期望的格式
        return result.values().stream().collect(Collectors.toList());
    }