solve problem Longest Word In Dictionary

Author: P-ppc

README.md

@@ -173,6 +173,7 @@ All solutions will be accepted!
 |860|[LemonadeChange](https://leetcode-cn.com/problems/lemonade-change/description/)|[java/py/js](./algorithms/LemonadeChange)|Easy|
 |401|[Binary Watch](https://leetcode-cn.com/problems/binary-watch/description/)|[java/py/js](./algorithms/BinaryWatch)|Easy|
 |482|[License Key Formatting](https://leetcode-cn.com/problems/license-key-formatting/description/)|[java/py/js](./algorithms/LicenseKeyFormatting)|Easy|
+|720|[Longest Word In Dictionary](https://leetcode-cn.com/problems/longest-word-in-dictionary/description/)|[java/py/js](./algorithms/LongestWordInDictionary)|Easy|
 
 # Database
 |#|Title|Solution|Difficulty|

algorithms/LongestWordInDictionary/README.md

@@ -0,0 +1,2 @@
+# Longest Word In Dictionary
+This problem is easy to solve by hashmap

algorithms/LongestWordInDictionary/Solution.java

@@ -0,0 +1,19 @@
+class Solution {
+    public String longestWord(String[] words) {
+        String longestWord = null;
+        Map<String, Boolean> wordsMap = new HashMap<String, Boolean>();
+        
+        Arrays.sort(words);
+        for (String word : words) {
+            int length = word.length();
+            if (length == 1 || wordsMap.get(word.substring(0, length - 1)) != null) {
+                wordsMap.put(word, true);
+                if (longestWord == null || longestWord.length() < length) {
+                    longestWord = word;
+                }
+            }
+        }
+        
+        return longestWord;
+    }
+}

algorithms/LongestWordInDictionary/solution.js

@@ -0,0 +1,18 @@
+/**
+ * @param {string[]} words
+ * @return {string}
+ */
+var longestWord = function(words) {
+    let longestWord = null,
+        wordsMap = {}
+    
+    words.sort().forEach(word => {
+        if (word.length === 1 || wordsMap[word.slice(0, word.length - 1)]) {
+            wordsMap[word] = true
+            if (!longestWord || word.length > longestWord.length) {
+                longestWord = word
+            }
+        }
+    })
+    return longestWord
+};

algorithms/LongestWordInDictionary/solution.py

@@ -0,0 +1,19 @@
+class Solution(object):
+    def longestWord(self, words):
+        """
+        :type words: List[str]
+        :rtype: str
+        """
+        words.sort()
+        
+        longest_word = None
+        words_map = {}
+        
+        for word in words:
+            if len(word) == 1 or words_map.get(word[:-1]) != None:
+                words_map[word] = True
+                if not longest_word or len(word) > len(longest_word):
+                    longest_word = word
+                
+        return longest_word
+