add Missing Number solution

Author: HoonDongKang

missing-number/HoonDongKang.ts

@@ -0,0 +1,26 @@
+/**
+ * [Problem]: [268] Missing Number
+ * (https://leetcode.com/problems/missing-number/description/)
+ */
+function missingNumber(nums: number[]): number {
+    //시간복잡도 O(n^2)
+    //공간복잡도 O(1)
+    function loopFunc(nums: number[]): number {
+        let num = 0;
+        while (true) {
+            if (!nums.includes(num)) break;
+            num++;
+        }
+
+        return num;
+    }
+    //시간복잡도 O(n)
+    //공간복잡도 O(1)
+    function sumFunc(nums: number[]): number {
+        const n = nums.length;
+        const sum = nums.reduce((acc, cur) => (acc += cur), 0);
+        const expected = (n * (n + 1)) / 2;
+
+        return expected - sum;
+    }
+}