Add solution #1228

JoshCrozier · JoshCrozier · commit 3919851e238d · 2025-06-28T00:37:47.000-05:00
diff --git a/README.md b/README.md
@@ -1,4 +1,4 @@
-# 2,350+ LeetCode solutions in JavaScript
+# 2,400+ LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -1140,6 +1140,7 @@
 1223|[Dice Roll Simulation](./solutions/1223-dice-roll-simulation.js)|Hard|
 1224|[Maximum Equal Frequency](./solutions/1224-maximum-equal-frequency.js)|Hard|
 1227|[Airplane Seat Assignment Probability](./solutions/1227-airplane-seat-assignment-probability.js)|Medium|
+1228|[Missing Number In Arithmetic Progression](./solutions/1228-missing-number-in-arithmetic-progression.js)|Easy|
 1232|[Check If It Is a Straight Line](./solutions/1232-check-if-it-is-a-straight-line.js)|Easy|
 1233|[Remove Sub-Folders from the Filesystem](./solutions/1233-remove-sub-folders-from-the-filesystem.js)|Medium|
 1234|[Replace the Substring for Balanced String](./solutions/1234-replace-the-substring-for-balanced-string.js)|Medium|
diff --git a/solutions/1228-missing-number-in-arithmetic-progression.js b/solutions/1228-missing-number-in-arithmetic-progression.js
@@ -0,0 +1,30 @@
+/**
+ * 1228. Missing Number In Arithmetic Progression
+ * https://leetcode.com/problems/missing-number-in-arithmetic-progression/
+ * Difficulty: Easy
+ *
+ * In some array arr, the values were in arithmetic progression: the values
+ * arr[i + 1] - arr[i] are all equal for every 0 <= i < arr.length - 1.
+ *
+ * A value from arr was removed that was not the first or last value in the array.
+ *
+ * Given arr, return the removed value.
+ */
+
+/**
+ * @param {number[]} arr
+ * @return {number}
+ */
+var missingNumber = function(arr) {
+  const n = arr.length;
+  const totalDiff = arr[n - 1] - arr[0];
+  const expectedDiff = totalDiff / n;
+
+  for (let i = 1; i < n; i++) {
+    if (arr[i] - arr[i - 1] !== expectedDiff) {
+      return arr[i - 1] + expectedDiff;
+    }
+  }
+
+  return arr[0] + expectedDiff;
+};
