Problem 208 (#33)

* add initial solution

* add refactored solution and resources

* update readme

Author: curtisbarnard

README.md

@@ -43,7 +43,7 @@ As I work through this list I figure I would make a GitHub repo with my solution
 32. [Clone Graph #133](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/clone-graph-133.md)
 33. [Evaluate Reverse Polish Notation #150](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/polish-notation-150.md)
 34. [Course Schedule #207](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/course-schedule-207.md)
-35. **Implement Trie (Prefix Tree) #208**
+35. [Implement Trie (Prefix Tree) #208](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/implement-trie-208.md)
 36. Coin Change #322
 37. Product of Array Except Self #238
 38. Min Stack #155
@@ -151,6 +151,7 @@ In order to practice with similar data structures I'll be placing each problem i
 - [3Sum #15](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/3Sum-15.md)
 - [Clone Graph #133](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/clone-graph-133.md)
 - [LRU Cache #146](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/lru-cache-146.md)
+- [Implement Trie (Prefix Tree) #208](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/implement-trie-208.md)
 
 ### Binary Tree
 
@@ -172,6 +173,10 @@ In order to practice with similar data structures I'll be placing each problem i
 - [K Closest Points to Origin #973](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/k-closest-origin-973.md)
 - [Meeting Rooms II](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/meeting-rooms-ii-253.md)
 
+### Trie
+
+- [Implement Trie (Prefix Tree) #208](https://github.com/curtisbarnard/leetcode-grind75-javascript/blob/main/medium/implement-trie-208.md)
+
 ## Algorithm Patterns
 
 Within the problems above there are several patterns that often occur. I plan to categorize each problem such that if you are having problem with a particular pattern you can look for other similar problems that use the same pattern.

medium/implement-trie-208.md

@@ -0,0 +1,177 @@
+# Implement Trie (Prefix Tree)
+
+Page on leetcode: https://leetcode.com/problems/implement-trie-prefix-tree/
+
+## Problem Statement
+
+A 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.
+
+### Constraints
+
+- 1 <= word.length, prefix.length <= 2000
+- word and prefix consist only of lowercase English letters.
+- At most 3 \* 104 calls in total will be made to insert, search, and startsWith.
+
+### Example
+
+```
+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
+```
+
+## Solution
+
+- root node val is empty
+- need a Node class?
+- Node class has list of next letters
+- Need some sort of flag for complete word
+- search traverse nodes and if it finds a matching node for each letter and last letter is a complete node will return true
+- starts with same as search except complete word not necessary
+
+### Pseudocode
+
+1. Create Node class with val, next letters, complete word
+2. Trie creates a node with no val, blank next letters and false complete word
+3. Insert takes string and puts into array
+4. Loops while array is not empty
+5. Checks if node contains letter as nextletter, if not add letter and go to it
+6. If array is empty then mark current node as complete word
+7. Search takes string and puts into array
+8. Loops while array is not empty
+9. Checks if node contains letter as nextletter, if not return false
+10. If array is empty and current node is a complete word return true, else return false
+11. StartsWith takes string and puts into array
+12. Loops while array is not empty
+13. Checks if node contains letter as nextletter, if not return false
+14. If array is empty return true
+
+### Initial Solution
+
+I believe this solution has a time complexity of O(n) for insert and search. Space complexity is O(n) for insertion and O(1) for search.
+
+```javascript
+const Node = function (val, completeWord) {
+  this.val = val;
+  this.completeWord = completeWord;
+  this.nextLetters = {};
+};
+
+const Trie = function () {
+  this.root = new Node(null, false);
+  return null;
+};
+
+Trie.prototype.insert = function (word) {
+  const wordArray = word.split('');
+  let currChar = this.root;
+  while (wordArray.length > 0) {
+    const char = wordArray.shift();
+    if (char in currChar.nextLetters) {
+      currChar = currChar.nextLetters[char];
+    } else {
+      currChar.nextLetters[char] = new Node(char, false);
+      currChar = currChar.nextLetters[char];
+    }
+  }
+  currChar.completeWord = true;
+  return null;
+};
+
+Trie.prototype.search = function (word) {
+  const wordArray = word.split('');
+  let currChar = this.root;
+  while (wordArray.length > 0) {
+    const char = wordArray.shift();
+    if (char in currChar.nextLetters) {
+      currChar = currChar.nextLetters[char];
+    } else {
+      return false;
+    }
+  }
+  if (currChar.completeWord) {
+    return true;
+  }
+  return false;
+};
+
+Trie.prototype.startsWith = function (prefix) {
+  const wordArray = prefix.split('');
+  let currChar = this.root;
+  while (wordArray.length > 0) {
+    const char = wordArray.shift();
+    if (char in currChar.nextLetters) {
+      currChar = currChar.nextLetters[char];
+    } else {
+      return false;
+    }
+  }
+  return true;
+};
+```
+
+### Optimized Solution
+
+The below is roughly the same as above, just with some clean up to make the code more concise. You can see an explanation for this solution here: https://www.youtube.com/watch?v=oobqoCJlHA0
+
+```javascript
+const Node = function () {
+  this.completeWord = false;
+  this.nextLetters = {};
+};
+
+const Trie = function () {
+  this.root = new Node();
+};
+
+Trie.prototype.insert = function (word) {
+  let cur = this.root;
+  for (char of word) {
+    if (!(char in cur.nextLetters)) {
+      cur.nextLetters[char] = new Node();
+    }
+    cur = cur.nextLetters[char];
+  }
+  cur.completeWord = true;
+};
+
+Trie.prototype.search = function (word) {
+  let cur = this.root;
+  for (char of word) {
+    if (!(char in cur.nextLetters)) {
+      return false;
+    }
+    cur = cur.nextLetters[char];
+  }
+  return cur.completeWord;
+};
+
+Trie.prototype.startsWith = function (prefix) {
+  let cur = this.root;
+  for (char of prefix) {
+    if (!(char in cur.nextLetters)) {
+      return false;
+    }
+    cur = cur.nextLetters[char];
+  }
+  return true;
+};
+```