implement trie

Author: fishercoder1534

MEDIUM/src/medium/ImplementTrie.java

@@ -0,0 +1,64 @@
+package medium;
+
+public class ImplementTrie {
+    class TrieNode {
+        
+        char val;
+        boolean isWord;
+        TrieNode[] children = new TrieNode[26];
+        
+        // Initialize your data structure here.
+        public TrieNode() {}
+        
+        public TrieNode(char c) {
+            this.val = c;
+        }
+    }
+
+    public class Trie {
+        private TrieNode root;
+
+        public Trie() {
+            root = new TrieNode();
+            root.val = ' ';//initialize root to be an empty char, this is a common practice as how Wiki defines Trie data structure as well
+        }
+
+        // Inserts a word into the trie.
+        public void insert(String word) {
+            TrieNode node = root;
+            for(int i = 0; i < word.length(); i++){
+                if(node.children[word.charAt(i) - 'a'] == null){
+                    node.children[word.charAt(i) - 'a'] = new TrieNode(word.charAt(i));
+                }
+                node = node.children[word.charAt(i) - 'a'];
+            }
+            node.isWord = true;
+        }
+
+        // Returns if the word is in the trie.
+        public boolean search(String word) {
+            TrieNode node = root;
+            for(int i = 0; i < word.length(); i++){
+                if(node.children[word.charAt(i) - 'a'] == null) return false;
+                node = node.children[word.charAt(i) - 'a'];
+            }
+            return node.isWord;
+        }
+
+        // Returns if there is any word in the trie
+        // that starts with the given prefix.
+        public boolean startsWith(String prefix) {
+            TrieNode node = root;
+            for(int i = 0; i < prefix.length(); i++){
+                if(node.children[prefix.charAt(i) - 'a'] == null) return false;
+                node = node.children[prefix.charAt(i) - 'a'];
+            }
+            return true;
+        }
+    }
+
+    // Your Trie object will be instantiated and called as such:
+    // Trie trie = new Trie();
+    // trie.insert("somestring");
+    // trie.search("key");
+}

README.md

@@ -6,6 +6,7 @@
 |441|[Arranging Coins](https://leetcode.com/problems/arrange-coins/)|[Solution](../../blob/master/EASY/src/easy/ArrangingCoins.java)| O(n)|O(1) | Easy|
 |436|[Find Right Interval](https://leetcode.com/problems/find-right-interval/)|[Solution](../../blob/master/MEDIUM/src/medium/FindRightInterval.java) | O(nlogn) |O(n) | Medium| Binary Search
 |435|[Non-overlapping Intervals](https://leetcode.com/problems/non-overlapping-intervals/)|[Solution](../../blob/master/MEDIUM/src/medium/NonOverlappingIntervals.java) | O(nlogn) |O(1) | Medium| Greedy
+|420|[Strong Password Checker](https://leetcode.com/problems/strong-password-checker/)|[Solution](../../blob/master/HARD/src/hard/StrongPasswordChecker.java)| ? | ? | Hard| 
 |419|[Battleships in a Board](https://leetcode.com/problems/battleships-in-a-board/)|[Solution](../../blob/master/MEDIUM/src/medium/BattleshipsinaBoard.java) | O(n^2) |O(1) | Medium| DFS
 |417|[Pacific Atlantic Water Flow](https://leetcode.com/problems/pacific-atlantic-water-flow/)|[Solution](../../blob/master/MEDIUM/src/medium/PacificAtlanticWaterFlow.java) | O(m*n*Max(m,n)) |O(m*n) | Medium| DFS
 |415|[Add Strings](https://leetcode.com/problems/add-strings/)|[Solution](../../blob/master/EASY/src/easy/AddStrings.java)| O(n)|O(1) | Easy|
@@ -39,6 +40,7 @@
 |223|[Rectangle Area](https://leetcode.com/problems/rectangle-area/)|[Solution](../../blob/master/EASY/src/easy/RectangleArea.java)| O(1)|O(1) | Easy| 
 |219|[Contains Duplicate II](https://leetcode.com/problems/contains-duplicate-ii/)|[Solution](../../blob/master/EASY/src/easy/ContainsDuplicateII.java)| O(n)|O(n) | Easy| HashMap
 |209|[Minimum Size Subarray Sum](https://leetcode.com/problems/minimum-size-subarray-sum/)|[Solution](../../blob/master/MEDIUM/src/medium/MinimumSizeSubarraySum.java)| O(n)|O(1) | Medium|
+|208|[Implement Trie](https://leetcode.com/problems/implement-trie-prefix-tree/)|[Solution](../../blob/master/MEDIUM/src/medium/ImplementTrie.java)| O(n)|O(1) | Medium|
 |206|[Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/)|[Solution](../../blob/master/EASY/src/easy/ReverseLinkedList.java)| O(n)|O(1) | Easy
 |205|[Isomorphic Strings](https://leetcode.com/problems/isomorphic-strings/)|[Solution](../../blob/master/EASY/src/easy/IsomorphicStrings.java)| O(n)|O(1) | Easy
 |200|[Number of Islands](https://leetcode.com/problems/number-of-islands/)|[Union Find](../../blob/master/MEDIUM/src/medium/NumberOfIslandsUnionFind.java) [DFS](../../blob/master/MEDIUM/src/medium/NumberofIslandsDFS.java)| O(m*n)|O(m*n) | Medium| Union Find, DFS