diff --git a/contains-duplicate/Real-Reason.kt b/contains-duplicate/Real-Reason.kt
new file mode 100644
index 000000000..c745379d3
--- /dev/null
+++ b/contains-duplicate/Real-Reason.kt
@@ -0,0 +1,10 @@
+package leetcode_study
+
+class SolutionContainsDuplicate {
+    fun containsDuplicate(nums: IntArray): Boolean {
+        val size = nums.size
+        val numsToSet = nums.toSet()
+
+        return size != numsToSet.size
+    }
+}
diff --git a/longest-consecutive-sequence/Real-Reason.kt b/longest-consecutive-sequence/Real-Reason.kt
new file mode 100644
index 000000000..d0f1c2c29
--- /dev/null
+++ b/longest-consecutive-sequence/Real-Reason.kt
@@ -0,0 +1,24 @@
+package leetcode_study
+class SolutionLongestConsecutiveSequence {
+    fun longestConsecutive(nums: IntArray): Int {
+        nums.sort()
+        var cnt = 0
+        var maxCnt = 0
+        nums.forEachIndexed { i, _ ->
+            if (i == 0) {
+                cnt = 1
+            }
+            else if (nums[i-1] == nums[i] - 1) {
+                cnt++
+            }
+            else if (nums[i - 1] == nums[i]) {
+                return@forEachIndexed
+            } else {
+                cnt = 1
+            }
+            maxCnt = maxOf(maxCnt, cnt)
+        }
+
+        return maxCnt
+    }
+}
diff --git a/top-k-frequent-elements/Real-Reason.kt b/top-k-frequent-elements/Real-Reason.kt
new file mode 100644
index 000000000..b88a28641
--- /dev/null
+++ b/top-k-frequent-elements/Real-Reason.kt
@@ -0,0 +1,15 @@
+package leetcode_study
+class SolutionTopKFrequentElements {
+    fun topKFrequent(nums: IntArray, k: Int): IntArray {
+        val numsCount = mutableMapOf<Int, Int>()
+        for (num in nums) {
+            val value = numsCount.getOrDefault(num, 0)
+            numsCount[num] = value + 1
+        }
+        val sortedNumsCount = numsCount.entries
+            .sortedByDescending { it.value }
+            .associate { it.toPair() }
+
+        return sortedNumsCount.keys.take(k).toIntArray()
+    }
+}
diff --git a/valid-palindrome/Real-Reason.kt b/valid-palindrome/Real-Reason.kt
new file mode 100644
index 000000000..23ae90f07
--- /dev/null
+++ b/valid-palindrome/Real-Reason.kt
@@ -0,0 +1,27 @@
+package leetcode_study
+
+class SolutionValidPalindrome {
+    fun isPalindrome(s: String): Boolean {
+        val sToCharArray = s.toCharArray()
+        var startIndex = 0
+        var endIndex = sToCharArray.size - 1
+        while (startIndex < endIndex) {
+            if (!sToCharArray[startIndex].isLetterOrDigit() || sToCharArray[startIndex].isWhitespace()) {
+                startIndex++
+                continue
+            }
+            if (!sToCharArray[endIndex].isLetterOrDigit() || sToCharArray[endIndex].isWhitespace()) {
+                endIndex--
+                continue
+            }
+            if (sToCharArray[startIndex].lowercase() == sToCharArray[endIndex].lowercase()) {
+                startIndex++
+                endIndex--
+            } else {
+                return false
+            }
+        }
+
+        return true
+    }
+}