Daily: 2026-10-21 — Contains Duplicate

automation/state.json

@@ -1,4 +1,4 @@
 {
-  "catalogIndex": 1,
-  "lastRunDate": "2026-10-20"
+  "catalogIndex": 2,
+  "lastRunDate": "2026-10-21"
 }

problems/2026-10-21-contains-duplicate/README.md

@@ -0,0 +1,24 @@
+# Contains Duplicate
+
+## Problem
+
+Given an integer array `nums`, return `true` if any value appears **at least twice** in the array, and return `false` if every element is distinct.
+
+## Examples
+
+```
+Input: nums = [1, 2, 3, 1]
+Output: true
+
+Input: nums = [1, 2, 3, 4]
+Output: false
+```
+
+## Constraints
+
+- `1 <= nums.length <= 10^5`
+- `-10^9 <= nums[i] <= 10^9`
+
+## Notes
+
+Implement `containsDuplicate` in `solution.js`.

problems/2026-10-21-contains-duplicate/contains-duplicate.test.js

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+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import { containsDuplicate } from "./solution.js";
+
+describe("containsDuplicate", () => {
+  it("has duplicate", () => {
+    assert.equal(containsDuplicate([1,2,3,1]), true);
+  });
+
+  it("all unique", () => {
+    assert.equal(containsDuplicate([1,2,3,4]), false);
+  });
+
+  it("duplicate at end", () => {
+    assert.equal(containsDuplicate([1,1]), true);
+  });
+});

problems/2026-10-21-contains-duplicate/solution.js

@@ -0,0 +1,12 @@
+/**
+ * @param {number[]} nums
+ * @returns {boolean}
+ */
+export function containsDuplicate(nums) {
+  const seen = new Set();
+  for (const n of nums) {
+    if (seen.has(n)) return true;
+    seen.add(n);
+  }
+  return false;
+}