Add missing-number solution in TS

Author: Jeehay28

missing-number/Jeehay28.ts

@@ -0,0 +1,30 @@
+// TC: O(n)
+// SC: O(1)
+function missingNumber(nums: number[]): number {
+  // 0, 1, 2, 3 => n * (n + 1) / 2
+
+  let sum = (nums.length * (nums.length + 1)) / 2;
+
+  for (const num of nums) {
+    sum -= num;
+  }
+
+  return sum;
+}
+
+
+// TC: O(n)
+// SC: (1)
+// function missingNumber(nums: number[]): number {
+//   let xor = 0;
+
+//   for (let i = 0; i <= nums.length; i++) {
+//     xor ^= i;
+//   }
+
+//   for (const num of nums) {
+//     xor ^= num;
+//   }
+
+//   return xor;
+// }