LeetCode 49. Group Anagrams（分组同构异形词）

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原题网址：https://leetcode.com/problems/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:

For the return value, each inner list's elements must follow the lexicographic order.
All inputs will be in lower-case.

方法：用histogram作为key，寻找同构词。

public class Solution {    public List<List<String>> groupAnagrams(String[] strs) {        List<List<String>> results = new ArrayList<>();        final char[][] sas = new char[strs.length][];        for(int i=0; i<strs.length; i++) sas[i] = strs[i].toCharArray();        List<Integer>[] keys = new List[strs.length];        for(int i=0; i<sas.length; i++) {            int[] f = new int[26];            for(int j=0; j<sas[i].length; j++) f[sas[i][j]-'a'] ++;            keys[i] = new ArrayList<>(26);            for(int k=0; k<26; k++) keys[i].add(f[k]);        }        Map<List<Integer>, List<String>> groups = new HashMap<>();        for(int i=0; i<strs.length; i++) {            List<String> anagrams = groups.get(keys[i]);            if (anagrams == null) {                anagrams = new ArrayList<>();                groups.put(keys[i], anagrams);            }            anagrams.add(strs[i]);        }        for(List<String> anagrams: groups.values()) {            Collections.sort(anagrams);            results.add(anagrams);        }        return results;    }}

另一种实现：

public class Solution {    public List<List<String>> groupAnagrams(String[] strs) {        Map<List<Integer>, List<String>> groups = new HashMap<>();        for(String s: strs) {            char[] sa = s.toCharArray();            Integer[] h = new Integer[26];            Arrays.fill(h, 0);            for(char c: sa) h[c-'a'] ++;            List<Integer> key = Arrays.asList(h);            List<String> group = groups.get(key);            if (group == null) {                group = new ArrayList<>();                groups.put(key, group);            }            group.add(s);        }        List<List<String>> results = new ArrayList<>();        results.addAll(groups.values());        return results;    }}

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