implemet trie

Author: chen0040

.idea/workspace.xml

@@ -420,3 +420,4 @@ codes may not be optimized
 
 1. [Longest Substring with at least k Repeating Characters](https://leetcode.com/problems/longest-substring-with-at-least-k-repeating-characters/description/)
 1. [Pacific Atlantic Water Flow](https://leetcode.com/problems/pacific-atlantic-water-flow/description/)
+1. [Implement Trie (Prefix Trie)](https://leetcode.com/problems/implement-trie-prefix-tree/description/)

README.md

@@ -0,0 +1,93 @@
+package com.github.chen0040.leetcode.day20.medium;
+
+
+/**
+ * Created by xschen on 15/8/2017.
+ *
+ * link: https://leetcode.com/problems/implement-trie-prefix-tree/description/
+ */
+public class ImplementTrie {
+   private static class Node {
+      boolean bit = false;
+      int key;
+      Node left;
+      Node right;
+      Node mid;
+      public Node(int key) {
+         this.key = key;
+      }
+   }
+
+   public class Trie {
+
+
+
+
+      private Node root;
+
+      /** Initialize your data structure here. */
+      public Trie() {
+
+      }
+
+      /** Inserts a word into the trie. */
+      public void insert(String word) {
+         root = insert(root, word, 0);
+      }
+
+      private Node insert(Node x, String word, int d) {
+         int key = (int)word.charAt(d);
+         if(x == null) {
+            x = new Node(key);
+         }
+
+         if(key < x.key){
+            x.left = insert(x.left, word, d);
+         } else if(key > x.key) {
+            x.right = insert(x.right, word, d);
+         } else {
+            if(d < word.length()-1) {
+               x.mid = insert(x.mid, word, d+1);
+            } else {
+               x.bit = true;
+            }
+         }
+
+         return x;
+      }
+
+      /** Returns if the word is in the trie. */
+      public boolean search(String word) {
+         Node x = get(root, word, 0);
+         if(x == null) {
+            return false;
+         } else {
+            return x.bit;
+         }
+      }
+
+      private Node get(Node x, String word, int d) {
+         if(x == null) {
+            return null;
+         }
+         int key = (int)word.charAt(d);
+         if(key < x.key) {
+            return get(x.left, word, d);
+         } else if(key > x.key) {
+            return get(x.right, word, d);
+         } else {
+            if(d == word.length()-1) {
+               return x;
+            } else {
+               return get(x.mid, word, d+1);
+            }
+         }
+      }
+
+      /** Returns if there is any word in the trie that starts with the given prefix. */
+      public boolean startsWith(String prefix) {
+         Node x = get(root, prefix, 0);
+         return x != null;
+      }
+   }
+}