feat: 268. Missing Number

Author: gwbaik9717

missing-number/gwbaik9717.js

@@ -0,0 +1,15 @@
+// Time complexity: O(n)
+// Space complexity: O(1)
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var missingNumber = function (nums) {
+  const n = nums.length;
+  const target = (n * (n + 1)) / 2;
+
+  const sum = nums.reduce((a, c) => a + c, 0);
+
+  return target - sum;
+};