Merge pull request #814 from Raven1233/main

Added 15-3Sum.kt and 208-Implement-Trie(Prefix-Tree).kt

Author: Ahmad-A0

kotlin/15-3Sum.kt

@@ -0,0 +1,43 @@
+class Solution {
+    fun threeSum(nums: IntArray): List<List<Int>> {
+        if(nums.size<3){
+            return List(0){List<Int>(0){0}}
+        }
+        if(nums.size==3){
+            return if(nums.sum()==0) listOf(nums.toList()) else List(0){List<Int>(0){0}}
+        }
+        nums.sort()
+        val a = MutableList(0){List(3){0}}
+        val s = nums.size
+        var j = 0
+        var k = 0
+        
+        for(i in 0 until s-2){
+            if(i!=0 && nums[i]==nums[i-1]){
+                continue
+            }
+            j = i+1
+            k = s-1
+            while(j<k){
+                if(nums[i]+nums[j]+nums[k]>0){
+                    k -= 1
+                }
+                else if(nums[i]+nums[j]+nums[k]<0){
+                    j += 1
+                }
+                else{
+                    a.add(listOf(nums[i], nums[j], nums[k]))
+                    j += 1
+                    k -= 1
+                    while(j<k && nums[j]==nums[j-1]){
+                        j+=1
+                    }
+                    while(k<j && nums[k]==nums[k+1]){
+                        k-=1
+                    }
+                }
+            }
+        }
+        return a
+    }
+}

kotlin/208-Implement-Trie.kt

@@ -0,0 +1,35 @@
+class Trie() {
+    private class Node {
+        val nxt = Array(26) { null as Node? }
+        var end = false
+    }
+    
+    private val root = Node()
+
+    fun insert(word: String) {
+        var cur = root
+        for (c in word) {
+            cur = cur.nxt[c - 'a'] ?: Node().also { cur.nxt[c - 'a'] = it }
+        }
+        cur.end = true
+    }
+
+    fun search(word: String): Boolean = internalSearch(word, prefix = false)
+
+    fun startsWith(prefix: String): Boolean = internalSearch(prefix, prefix = true)
+    
+    private fun internalSearch(word: String, prefix: Boolean): Boolean {
+        var cur = root
+        for (c in word) {
+            cur = cur.nxt[c - 'a'] ?: return false
+        }
+        return cur.end || prefix
+    }
+}
+/**
+ * Your Trie object will be instantiated and called as such:
+ * var obj = Trie()
+ * obj.insert(word)
+ * var param_2 = obj.search(word)
+ * var param_3 = obj.startsWith(prefix)
+ */