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Commit 3d90a93

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solves trie #208 in java
1 parent 6e51450 commit 3d90a93

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3 files changed

+67
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3 files changed

+67
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‎README.md‎

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| 205 | [Isomorphic Strings](https://leetcode.com/problems/isomorphic-strings) | [![Java](assets/java.png)](src/IsomorphicStrings.java) [![Python](assets/python.png)](python/isomorphic_strings.py) | |
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| 206 | [Reverse Linked List](https://leetcode.com/problems/reverse-linked-list) | [![Java](assets/java.png)](src/ReverseLinkedList.java) [![Python](assets/python.png)](python/reverse_linked_list.py) | |
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| 207 | [Course Schedule](https://leetcode.com/problems/course-schedule) | [![Java](assets/java.png)](src/CourseSchedule.java) | |
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| 208 | [Implement Trie (Prefix Tree)](https://leetcode.com/problems/implement-trie-prefix-tree) | | |
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| 208 | [Implement Trie (Prefix Tree)](https://leetcode.com/problems/implement-trie-prefix-tree) | [![Java](assets/java.png)](src/Trie.java) | |
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| 209 | [Minimum Size Subarray Sum](https://leetcode.com/problems/minimum-size-subarray-sum) | | |
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| 210 | [Course Schedule II](https://leetcode.com/problems/course-schedule-ii) | | |
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| 211 | [Design Add and Search Words Data Structure](https://leetcode.com/problems/design-add-and-search-words-data-structure) | | |

‎src/HelloWorld.java‎

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public class HelloWorld {
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public static void main(String[] args) {
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System.out.println("Hello world");
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Trie trie = new Trie();
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trie.insert("apple");
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// System.out.println(trie.search("apple"));
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// System.out.println(trie.search("app"));
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System.out.println(trie.startsWith("app")); // true
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trie.insert("app");
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// System.out.println(trie.search("app"));
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}
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}

‎src/Trie.java‎

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// https://leetcode.com/problems/implement-trie-prefix-tree
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// insertion
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// T: O(n)
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// S: O(n)
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// search
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// T: O(n)
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// S: O(n)
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// starts with
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// T: O(n)
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// S: O(n)
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public class Trie {
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private final Trie[] alphabet = new Trie[26];
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private boolean isWordEnd = false;
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public Trie() { }
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public void insert(String word) {
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insert(word, 0);
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}
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private void insert(String word, int index) {
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if (index == word.length()) {
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this.isWordEnd = true;
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return;
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}
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int charIndex = toIndex(word.charAt(index));
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if (alphabet[charIndex] == null) {
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alphabet[charIndex] = new Trie();
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}
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alphabet[charIndex].insert(word, index + 1);
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}
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public boolean search(String word) {
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return search(word, 0);
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}
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public boolean search(String word, int index) {
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if (index == word.length()) return isWordEnd;
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int charIndex = toIndex(word.charAt(index));
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if (alphabet[charIndex] == null) return false;
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return alphabet[charIndex].search(word, index + 1);
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}
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public boolean startsWith(String prefix) {
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return startsWith(prefix, 0);
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}
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public boolean startsWith(String prefix, int index) {
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if (index == prefix.length()) return true;
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int charIndex = toIndex(prefix.charAt(index));
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if (alphabet[charIndex] == null) return false;
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return alphabet[charIndex].startsWith(prefix, index + 1);
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}
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private int toIndex(char c) {
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return c - 'a';
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}
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}

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