[hyunjung-choi] WEEK 01 solutions

contains-duplicate/hyunjung-choi.kt

@@ -0,0 +1,5 @@
+class Solution {
+    fun containsDuplicate(nums: IntArray): Boolean {
+        return nums.size != nums.toSet().size
+    }
+}

house-robber/hyunjung-choi.kt

@@ -0,0 +1,18 @@
+package leetcode_study
+
+class Solution {
+    fun rob(nums: IntArray): Int {
+        if (nums.size == 1) return nums[0]
+
+        var prev2 = nums[0]
+        var prev1 = maxOf(nums[0], nums[1])
+
+        for (i in 2 until nums.size) {
+            val current = maxOf(prev1, prev2 + nums[i])
+            prev2 = prev1
+            prev1 = current
+        }
+
+        return prev1
+    }
+}

longest-consecutive-sequence/hyunjung-choi.kt

@@ -0,0 +1,24 @@
+package leetcode_study
+
+class Solution {
+    fun longestConsecutive(nums: IntArray): Int {
+        if (nums.isEmpty()) return 0
+
+        val sortedNums = nums.sorted()
+        var maxLength = 1
+        var currentLength = 1
+
+        for (i in 1 until sortedNums.size) {
+            when {
+                sortedNums[i] == sortedNums[i - 1] -> continue
+                sortedNums[i] == sortedNums[i - 1] + 1 -> {
+                    currentLength++
+                    maxLength = maxOf(maxLength, currentLength)
+                }
+                else -> currentLength = 1
+            }
+        }
+
+        return maxLength
+    }
+}

top-k-frequent-elements/hyunjung-choi.kt

@@ -0,0 +1,12 @@
+class Solution {
+    fun topKFrequent(nums: IntArray, k: Int): IntArray {
+        val frequency = nums.toList().groupingBy { it }.eachCount()
+
+        return frequency
+            .toList()
+            .sortedByDescending { it.second }
+            .take(k)
+            .map { it.first }
+            .toIntArray()
+    }
+}

two-sum/hyunjung-choi.kt

@@ -0,0 +1,16 @@
+class Solution {
+    fun twoSum(nums: IntArray, target: Int): IntArray {
+        val result = IntArray(2)
+
+        for (i in nums.indices) {
+            for (j in i + 1 until nums.size) {
+                if (nums[i] + nums[j] == target) {
+                    result[0] = i
+                    result[1] = j
+                }
+            }
+        }
+
+        return result
+    }
+}