init commit

Author: yuanyu90221

.github/workflows/java.yml

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+name: Java
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Setup JDK 11
+        uses: actions/setup-java@v3
+        with:
+          distribution: 'adopt'
+          java-version: '11'
+      - name: Grant execution permission for gradlew
+        run: chmod +x gradlew
+      - name: Cache Gradle packages
+        uses: actions/cache@v3
+        with:
+          path: ~/.gradle/caches
+          key: ${{ runner.os }}-gradle-${{ github.event.repository.name }}-${{ hashFiles('**/*.gradle')}}
+          restore-keys: ${{ runner.os }}-gradle-${{ github.event.repository.name }}
+      - name: Build with Gradlew
+        run: ./gradlew build
+      - name: Test with Gradlew
+        run: ./gradlew :test --tests "SolutionTest"

.gitignore

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+.gradle
+build/
+!gradle/wrapper/gradle-wrapper.jar
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### IntelliJ IDEA ###
+.idea/modules.xml
+.idea/jarRepositories.xml
+.idea/compiler.xml
+.idea/libraries/
+*.iws
+*.iml
+*.ipr
+out/
+!**/src/main/**/out/
+!**/src/test/**/out/
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+bin/
+!**/src/main/**/bin/
+!**/src/test/**/bin/
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store

.husky/pre-commit

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+#!/bin/bash
+./gradlew :test --tests "SolutionTest"

.idea/gradle.xml

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+# java_implement_trie
+
+A **[trie](https://en.wikipedia.org/wiki/Trie)** (pronounced as "try") or **prefix tree** is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure, such as autocomplete and spellchecker.
+
+Implement the Trie class:
+
+- `Trie()` Initializes the trie object.
+- `void insert(String word)` Inserts the string `word` into the trie.
+- `boolean search(String word)` Returns `true` if the string `word` is in the trie (i.e., was inserted before), and `false` otherwise.
+- `boolean startsWith(String prefix)` Returns `true` if there is a previously inserted string `word` that has the prefix `prefix`, and `false` otherwise.
+
+## Examples
+
+**Example 1:**
+
+```
+Input
+["Trie", "insert", "search", "search", "startsWith", "insert", "search"]
+[[], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]]
+Output
+[null, null, true, false, true, null, true]
+
+Explanation
+Trie trie = new Trie();
+trie.insert("apple");
+trie.search("apple");   // return True
+trie.search("app");     // return False
+trie.startsWith("app"); // return True
+trie.insert("app");
+trie.search("app");     // return True
+
+```
+
+**Constraints:**
+
+- `1 <= word.length, prefix.length <= 2000`
+- `word` and `prefix` consist only of lowercase English letters.
+- At most $`3*10^4`$ calls **in total** will be made to `insert`, `search`, and `startsWith`.
+
+## 解析
+
+題目要我們實作一個可以儲存所有小寫英文字的一個 Trie結構
+
+需要實作出以下 method:
+
+1.  Constructor:  用來來建構 Trie
+2.  insert(word string): 用來儲存 word
+3. search(word string) bool: 用來察看是否有儲存過這個 word
+4. startsWith(prefix string) bool:  用來察看是否有儲存過包含 prefix 的 word
+
+首先知道 Trie 是一種特殊的 Tree
+
+目前需要儲存所有字元是小寫英文 a-z 組成的字串
+
+為了節省空間所以會是已字元為單位來做存儲
+
+另外是可以透過把 字元當成每個 node 的 edge 上 key
+
+如下圖：
+
+![](https://i.imgur.com/JTyTsFg.png)
+
+每個結點都可以透過 key 來找到下一個結點
+
+這個結構可以使用 hashmap 來實作
+
+而沒每個結點除了這個用來紀錄 child 對應的 hashmap 外
+
+需要一個布林值來紀錄這個結點是否為最後一個結點
+
+如上圖的 Trie 雖然有 appl 的 prefix 但是卻沒有 appl 這個字
+
+## 程式碼
+
+```java
+public class Trie {
+  static class TrieNode {
+    boolean EndOfWord = false;
+    HashMap<Character, TrieNode> Children = new HashMap<>();
+  }
+  TrieNode root;
+  public Trie() {
+    root = new TrieNode();
+  }
+  public void insert(String word) {
+    TrieNode cur = root;
+    int size = word.length();
+    for (int pos = 0; pos < size; pos++) {
+      char ch = word.charAt(pos);
+      if (!cur.Children.containsKey(ch)) {
+        cur.Children.put(ch, new TrieNode());
+      }
+      cur = cur.Children.get(ch);
+    }
+    cur.EndOfWord = true;
+  }
+  public boolean search(String word) {
+    TrieNode cur = root;
+    int size = word.length();
+    for (int pos = 0; pos < size; pos++) {
+      char ch = word.charAt(pos);
+      if (!cur.Children.containsKey(ch)) {
+        return false;
+      }
+      cur = cur.Children.get(ch);
+    }
+    return cur.EndOfWord;
+  }
+  public boolean startsWith(String prefix) {
+    TrieNode cur = root;
+    int size = prefix.length();
+    for (int pos = 0; pos < size; pos++) {
+      char ch = prefix.charAt(pos);
+      if (!cur.Children.containsKey(ch)) {
+        return false;
+      }
+      cur = cur.Children.get(ch);
+    }
+    return true;
+  }
+}
+```
+
+## 困難點
+
+1. 轉換紀錄 edge的值當作 index
+
+## Solve Point
+
+- [x]  Understand What problem need to solve
+- [x]  Analysis complexity