diff --git a/missing-number/Lustellz.ts b/missing-number/Lustellz.ts
new file mode 100644
index 000000000..f114f107d
--- /dev/null
+++ b/missing-number/Lustellz.ts
@@ -0,0 +1,21 @@
+// Runtime: 18ms
+// Memory: 58.64MB
+
+function missingNumber(nums: number[]): number {
+    const sortedNums: number[] = nums.sort((a, b) => a - b);
+    for(let i = 0; i <= nums.length; i++){
+        if(sortedNums[i] !== i) return i
+    }
+};
+
+// Runtime: 1ms
+// Memory: 58.34MB
+// reduce sum of array to find missing number
+
+function missingNumber(nums: number[]): number {
+    const n: number = nums.length;
+    const numSum: number = nums.reduce((acc, cur) => (acc += cur), 0);
+    const expectedSum: number = (n * (n + 1)) / 2;
+
+    return expectedSum - numSum;
+}