feat: solve 5 week algorithm

Author: Real-Reason

best-time-to-buy-and-sell-stock/Real-Reason.kt

@@ -0,0 +1,15 @@
+package leetcode_study
+
+import kotlin.math.max
+import kotlin.math.min
+fun maxProfit(prices: IntArray): Int {
+    var minPrice = prices[0]
+    var maxProfit = 0
+
+    for (i in 0 until prices.size) {
+        maxProfit = max(maxProfit, prices[i] - minPrice)
+        minPrice = min(minPrice, prices[i])
+    }
+
+    return maxProfit
+}

group-anagrams/Real-Reason.kt

@@ -0,0 +1,13 @@
+package leetcode_study
+
+fun groupAnagrams(strs: Array<String>): List<List<String>> {
+    val anagrams = HashMap<String, MutableList<String>>()
+    strs.forEach { str ->
+        val chars = str.toCharArray().sorted()
+        anagrams.putIfAbsent(chars.toString(), mutableListOf())
+        val words = anagrams[chars.toString()]
+        words?.add(str)
+    }
+
+    return anagrams.values.toList()
+}

implement-trie-prefix-tree/Real-Reason.kt

@@ -0,0 +1,59 @@
+package leetcode_study
+
+class FirstSolution {
+    private val document = hashSetOf<String>()
+
+    fun insert(word: String) {
+        document.add(word)
+    }
+
+    fun search(word: String): Boolean {
+        return document.contains(word)
+    }
+
+    fun startsWith(prefix: String): Boolean {
+        val word = document.firstOrNull { it.startsWith(prefix) }
+        return word != null
+    }
+}
+
+class SecondSolution {
+    class Document(var end: Boolean = true) {
+        val items = hashMapOf<Char, Document>()
+    }
+
+    private val document = Document(end = true)
+
+    fun insert(word: String) {
+        var node = document
+        for (char in word) {
+            if (char !in node.items) {
+                node.items[char] = Document(end = false)
+            }
+            node = node.items[char]!!
+        }
+        node.end = true
+    }
+
+    fun search(word: String): Boolean {
+        var node = document
+        for (char in word) {
+            if (char !in node.items) {
+                return false
+            }
+            node = node.items[char]!!
+        }
+        return node.end
+    }
+
+    fun startsWith(prefix: String): Boolean {
+        var node = document
+        for (char in prefix) {
+            if (char !in node.items) {
+                return false
+            }
+            node = node.items[char]!!
+        }
+        return true
+    }
+}