Missing Number Solution

Author: naringst

missing-number/naringst.js

@@ -0,0 +1,45 @@
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+
+/**
+ * Runtime: 63ms, Memory: 51.68MB
+ * Time complexity: O(nlogn)
+ * Space complexity: O(nlogn)
+ *
+ */
+
+var missingNumber = function (nums) {
+  const n = nums.length;
+  nums.sort((a, b) => a - b);
+
+  if (!nums.includes(0)) {
+    return 0;
+  }
+  for (let i = 0; i < n; i++) {
+    if (nums[i + 1] - nums[i] !== 1) {
+      return nums[i] + 1;
+    }
+  }
+  return nums[-1];
+};
+
+/**
+ * NOTE
+ * if use 'sort()' -> O(nlogn)
+ * if you solve this problem without using sort(), can use sum of nums
+ */
+
+var missingNumber = function (nums) {
+  const sumOfNums = nums.reduce((num, total) => num + total, 0);
+
+  const n = nums.length;
+  const expectedSum = (n * (n + 1)) / 2;
+
+  if (expectedSum === sumOfNums) {
+    return 0;
+  } else {
+    return expectedSum - sumOfNums;
+  }
+};