208. Implement Trie (Prefix Tree)

Author: BGMer7

src/com/gatsby/_208ImplementTrie.java

@@ -0,0 +1,55 @@
+package com.gatsby;
+
+/**
+ * @author -- gatsby
+ * @date -- 2022/7/12
+ * @description --
+ */
+
+
+public class _208ImplementTrie {
+    class TrieNode {
+        boolean isEnd = false;
+        // 直接创建一个26字母的数组，这样已经可以考虑到所有的下一位字母的情况
+        TrieNode[] children = new TrieNode[26];
+    }
+
+    private TrieNode root;
+
+    public _208ImplementTrie() {
+        root = new TrieNode();
+    }
+
+    public void insert(String word) {
+        TrieNode p = root;
+        for (int i = 0; i < word.length(); ++i) {
+            int letter = word.charAt(i) - 'a';
+            if (p.children[letter] == null) {
+                p.children[letter] = new TrieNode();
+            }
+            p = p.children[letter];
+        }
+        // 此时在最后一个字母，将isEnd置为true
+        p.isEnd = true;
+    }
+
+    public boolean search(String word) {
+        TrieNode p = root;
+        for (int i = 0; i < word.length(); ++i) {
+            int letter = word.charAt(i) - 'a';
+            if (p.children[letter] == null) return false;
+            else p = p.children[letter];
+        }
+        return p.isEnd;
+    }
+
+    public boolean startsWith(String prefix) {
+        TrieNode p = root;
+        for (int i = 0; i < prefix.length(); ++i) {
+            int letter = prefix.charAt(i) - 'a';
+            if (p.children[letter] == null) return false;
+            else p = p.children[letter];
+        }
+        return true;
+    }
+}