LeetCode: Anagrams 解题报告

Anagrams
Given an array of strings, return all groups of strings that are anagrams.

Note: All inputs will be in lower-case.

思路：

建Hashtable，用排序过的string作为key，它的anagram作为ArrayList

这道题之前用暴力写的O(N^2)的TLE了，改用Hashtable来写
题目的意思是给一个String数组，找出其中由相同字母组成的单词。
例如：
S = ["abc", "bca", "bac", "bbb", "bbca", "abcb"]
答案为：
["abc", "bca", "bac", "bbca", "abcb"]
只有"bbb"没有相同字母组成的单词。

ref: http://blog.csdn.net/fightforyourdream/article/details/14217985

public class Solution {
    public List<String> anagrams(String[] strs) {
        List<String> ret = new ArrayList<String>();
        
        if (strs == null) {
            return ret;
        }
        
        HashMap<String, List<String>> map = new HashMap<String, List<String>>();
        
        int len = strs.length;
        for (int i = 0; i < len; i++) {
            String s = strs[i];
            
            // Sort the string.            
            char[] chars = s.toCharArray();
            Arrays.sort(chars);
            String strSort = new String(chars);   
            
            // Create a ArrayList for the sorted string.            
            if (!map.containsKey(strSort)) {
                map.put(strSort, new ArrayList<String>());
            }
            
            // Add a new string to the list of the hashmap.
            map.get(strSort).add(s);
        }
        
        // go through the map and add all the strings into the result.
        for (Map.Entry<String, List<String>> entry: map.entrySet()) {
            List<String> list = entry.getValue();
            
            // skip the entries which only have one string.
            if (list.size() == 1) {
                continue;
            }
            
            // add the strings into the list.
            ret.addAll(list);
        }
        
        return ret;
    }
}

2015.1.3 redo:

public class Solution {
    public List<String> anagrams(String[] strs) {
        List<String> ret = new ArrayList<String>();
        if (strs == null) {
            return ret;
        }
        
        HashMap<String, List<String>> map = new HashMap<String, List<String>>();
        for (int i = 0; i < strs.length; i++) {
            String s = strs[i];
            char[] chars = s.toCharArray();
            
            Arrays.sort(chars);
            String sSort = new String(chars);
            
            if (map.containsKey(sSort)) {
                map.get(sSort).add(s);
            } else {
                List<String> list = new ArrayList<String>();
                list.add(s);
                map.put(sSort, list);
            }
        }
        
        // Bug 1: should use map.entrySet() instead of MAP.
        for (Map.Entry<String, List<String>> entry: map.entrySet()) {
            List<String> list = entry.getValue();
            if (list.size() > 1) {
                ret.addAll(list);
            }
        }
        
        return ret;
    }
}

https://github.com/yuzhangcmu/LeetCode_algorithm/blob/master/hash/Anagrams.java