diff --git a/contest/src/main/java/com/github/contest/Execute.kt b/contest/src/main/java/com/github/contest/Execute.kt
index 23b2a76a..fd25f043 100644
--- a/contest/src/main/java/com/github/contest/Execute.kt
+++ b/contest/src/main/java/com/github/contest/Execute.kt
@@ -1,7 +1,9 @@
 package com.github.contest
 
 
+import com.github.contest.bitManipulation.subsetXORSum
 import com.github.contest.strings.shiftingLetters
+import com.github.contest.strings.smallestStringProdVariant
 
 import java.util.TreeMap
 
@@ -12,7 +14,7 @@ import java.util.TreeMap
 
 fun main() {
 
-    shiftingLetters("abc", intArrayOf(3, 5, 9)).also { println(it) }
+    subsetXORSum(intArrayOf(5, 1, 6))
 }
 
 fun testing() {
diff --git a/contest/src/main/java/com/github/contest/bitManipulation/BitManipulationLeetcode.kt b/contest/src/main/java/com/github/contest/bitManipulation/BitManipulationLeetcode.kt
index 11c0275f..e3a63857 100644
--- a/contest/src/main/java/com/github/contest/bitManipulation/BitManipulationLeetcode.kt
+++ b/contest/src/main/java/com/github/contest/bitManipulation/BitManipulationLeetcode.kt
@@ -1,2 +1,25 @@
 package com.github.contest.bitManipulation
 
+/**
+ * 1863. Sum of All Subset XOR Totals
+ */
+
+fun subsetXORSum(nums: IntArray): Int {
+    var totalXORSum = 0
+
+    fun calculateSubsetXOR(index: Int, currentXOR: Int) {
+        if (index == nums.size) {
+            totalXORSum += currentXOR
+            return
+        }
+
+        // Include the current element
+        calculateSubsetXOR(index + 1, currentXOR xor nums[index])
+
+        // Exclude the current element
+        calculateSubsetXOR(index + 1, currentXOR)
+    }
+
+    calculateSubsetXOR(0, 0)
+    return totalXORSum
+}
\ No newline at end of file
diff --git a/contest/src/main/java/com/github/contest/hashTable/HashTableLeetcode.kt b/contest/src/main/java/com/github/contest/hashTable/HashTableLeetcode.kt
index 6556bc79..aaf90379 100644
--- a/contest/src/main/java/com/github/contest/hashTable/HashTableLeetcode.kt
+++ b/contest/src/main/java/com/github/contest/hashTable/HashTableLeetcode.kt
@@ -256,4 +256,19 @@ fun findMissingAndRepeatedValues(grid: Array<IntArray>): IntArray {
     }
 
     return res
+}
+
+/**
+ * 2351. First Letter to Appear Twice
+ */
+
+fun repeatedCharacter(s: String): Char {
+    val alphabet = IntArray(26)
+    for (char in s) {
+        val index = char - 'a'
+        if (alphabet[index] == 0) alphabet[index] += 1
+        else return char
+    }
+
+    return 'a'
 }
\ No newline at end of file
diff --git a/contest/src/main/java/com/github/contest/strings/StringsAlternativeSolution.kt b/contest/src/main/java/com/github/contest/strings/StringsAlternativeSolution.kt
new file mode 100644
index 00000000..f9382ac4
--- /dev/null
+++ b/contest/src/main/java/com/github/contest/strings/StringsAlternativeSolution.kt
@@ -0,0 +1,2 @@
+package com.github.contest.strings
+
diff --git a/contest/src/main/java/com/github/contest/strings/StringsLeetcode.kt b/contest/src/main/java/com/github/contest/strings/StringsLeetcode.kt
index bbba6e3a..c3f38ce1 100644
--- a/contest/src/main/java/com/github/contest/strings/StringsLeetcode.kt
+++ b/contest/src/main/java/com/github/contest/strings/StringsLeetcode.kt
@@ -5,13 +5,18 @@ package com.github.contest.strings
  */
 
 fun shiftingLetters(str: String, shifts: IntArray): String {
-    val shifting = IntArray(shifts.size)
-    var sum = shifts.sum()
+    val shifting = LongArray(shifts.size)
+    var sum = 0L
     var res = ""
 
+    for (element in shifts) {
+        val num = element.toLong()
+        sum += num
+    }
+
     for (i in shifting.indices) {
         shifting[i] = sum
-        sum -= shifts[i]
+        sum -= shifts[i].toLong()
     }
 
     for (i in str.indices) {
@@ -23,13 +28,65 @@ fun shiftingLetters(str: String, shifts: IntArray): String {
     return res
 }
 
-private fun shiftLetter(char: Char, shift: Int): Char = when {
+private fun shiftLetter(char: Char, shift: Long): Char = when {
     char in 'a'..'z' -> {
         val base = 'a'.code
         val offset = char.code - base
         val shifted = (offset + shift) % 26
         (base + shifted).toChar()
     }
+
     else -> char
 }
 
+/**
+ * 2734. Lexicographically Smallest String After Substring Operation
+ */
+
+fun smallestString(s: String): String {
+    if (s.hasSingle()) return when {
+        s[0] == 'a' -> 'z'.toString()
+        else -> Char(s[0].code - 1).toString()
+    }
+    val chars = s.toCharArray()
+    val n = chars.size
+    var start = -1
+
+    for (i in 0 until n) {
+        if (chars[i] != 'a') {
+            start = i
+            break
+        }
+    }
+
+    if (start == -1) {
+        chars[n - 1] = 'z'
+        return String(chars)
+    }
+
+    for (i in start until n) {
+        if (chars[i] != 'a') chars[i]--
+        else break
+    }
+
+    return String(chars)
+
+}
+
+fun String.hasSingle(): Boolean = when {
+    this.length == 1 -> true
+    else -> false
+}
+
+/**
+ * 2278. Percentage of Letter in String
+ */
+
+fun percentageLetter(s: String, letter: Char): Int {
+    var count = 0
+    for (char in s) if (char == letter) count++
+    return if (count == 0) 0 else (count * 100) / s.length
+}
+
+
+
diff --git a/contest/src/main/java/com/github/contest/strings/StringsProdVariant.kt b/contest/src/main/java/com/github/contest/strings/StringsProdVariant.kt
new file mode 100644
index 00000000..f94a8152
--- /dev/null
+++ b/contest/src/main/java/com/github/contest/strings/StringsProdVariant.kt
@@ -0,0 +1,61 @@
+package com.github.contest.strings
+
+/**
+ * 848. Shifting Letters
+ * Prod Variant
+ */
+
+fun shiftingLetterProdVariant(str: String, shifts: IntArray): String {
+    var sum = shifts.toLongArray().sum()
+    return buildString {
+        str.forEachIndexed { index, letter ->
+            val new = letter.shiftLetter(sum)
+            append(new)
+            sum -= shifts[index]
+        }
+    }
+}
+
+private fun IntArray.toLongArray(): LongArray {
+    val new = LongArray(this.size)
+    for (i in indices) {
+        new[i] = this[i].toLong()
+    }
+
+    return new
+}
+
+private fun Char.shiftLetter(shift: Long): Char = when {
+    this in 'a'..'z' -> {
+        val base = 'a'.code
+        val offset = this.code - base
+        val shifted = (offset + shift) % 26
+        (base + shifted).toChar()
+    }
+
+    else -> this
+}
+
+/**
+ * 2734. Lexicographically Smallest String After Substring Operation
+ * Prod Variant
+ */
+
+fun smallestStringProdVariant(s: String): String {
+    val firstNonAIndex = s.indexOfFirst { it != 'a' }
+
+    return if (firstNonAIndex == -1) {
+        s.dropLast(1) + 'z'
+    } else {
+        val modifiedChars = s.toCharArray().also { chars ->
+            for (i in firstNonAIndex until chars.size) {
+                if (chars[i] != 'a') {
+                    chars[i]--
+                } else {
+                    break
+                }
+            }
+        }
+        String(modifiedChars)
+    }
+}
\ No newline at end of file