feat(curriculum): daily challenges 279-294 (freeCodeCamp#67227)

Author: moT01

curriculum/challenges/english/blocks/daily-coding-challenges-javascript/69f35a5bb823ed620fcb7cb8.md

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+---
+id: 69f35a5bb823ed620fcb7cb8
+title: "Challenge 279: Longest Domino Chain"
+challengeType: 28
+dashedName: challenge-279
+---
+
+# --description--
+
+Given a 2D array representing a set of dominoes, return the longest valid chain.
+
+- Each domino is a pair of numbers from 0–6, e.g. `[3, 2]`.
+- A chain is valid when the second number of each domino matches the first number of the next.
+- The first number of the first domino and the second number of the last one don't need to match anything.
+- Any domino can be flipped, so `[3, 2]` can be played as `[2, 3]`.
+- There is always exactly one longest valid chain.
+
+For example, given `[[1, 2], [4, 5], [2, 3]]`, return `[[1, 2], [2, 3]]`.
+
+# --hints--
+
+`getLongestChain([[1, 2], [4, 5], [2, 3]])` should return `[[1, 2], [2, 3]]`.
+
+```js
+const chain = JSON.stringify(getLongestChain([[1, 2], [4, 5], [2, 3]]));
+const result1 = JSON.stringify([[1, 2], [2, 3]]);
+const result2 = JSON.stringify([[3, 2], [2, 1]]);
+assert.isTrue(chain === result1 || chain === result2);
+```
+
+`getLongestChain([[2, 1], [4, 3], [5, 3]])` should return `[[4, 3], [3, 5]]`.
+
+```js
+const chain = JSON.stringify(getLongestChain([[2, 1], [4, 3], [5, 3]]));
+const result1 = JSON.stringify([[4, 3], [3, 5]]);
+const result2 = JSON.stringify([[5, 3], [3, 4]]);
+assert.isTrue(chain === result1 || chain === result2);
+```
+
+`getLongestChain([[1, 2], [3, 4], [2, 3], [4, 0]])` should return `[[1, 2], [2, 3], [3, 4], [4, 0]]`.
+
+```js
+const chain = JSON.stringify(getLongestChain([[1, 2], [3, 4], [2, 3], [4, 0]]));
+const result1 = JSON.stringify([[1, 2], [2, 3], [3, 4], [4, 0]]);
+const result2 = JSON.stringify([[0, 4], [4, 3], [3, 2], [2, 1]]);
+assert.isTrue(chain === result1 || chain === result2);
+```
+
+`getLongestChain([[6, 6], [6, 1], [1, 1], [0, 3], [2, 3], [4, 1], [5, 6]])` should return `[[4, 1], [1, 1], [1, 6], [6, 6], [6, 5]]`.
+
+```js
+const chain = JSON.stringify(getLongestChain([[6, 6], [6, 1], [1, 1], [0, 3], [2, 3], [4, 1], [5, 6]]));
+const result1 = JSON.stringify([[4, 1], [1, 1], [1, 6], [6, 6], [6, 5]]);
+const result2 = JSON.stringify([[5, 6], [6, 6], [6, 1], [1, 1], [1, 4]]);
+assert.isTrue(chain === result1 || chain === result2);
+```
+
+`getLongestChain([[0, 4], [3, 3], [0, 3], [5, 6], [4, 5], [4, 2], [5, 5], [1, 2], [4, 4]])` should return `[[3, 3], [3, 0], [0, 4], [4, 4], [4, 5], [5, 5], [5, 6]]`.
+
+```js
+const chain = JSON.stringify(getLongestChain([[0, 4], [3, 3], [0, 3], [5, 6], [4, 5], [4, 2], [5, 5], [1, 2], [4, 4]]));
+const result1 = JSON.stringify([[3, 3], [3, 0], [0, 4], [4, 4], [4, 5], [5, 5], [5, 6]]);
+const result2 = JSON.stringify([[6, 5], [5, 5], [5, 4], [4, 4], [4, 0], [0, 3], [3, 3]]);
+assert.isTrue(chain === result1 || chain === result2);
+```
+
+# --seed--
+
+## --seed-contents--
+
+```js
+function getLongestChain(dominoes) {
+
+  return dominoes;
+}
+```
+
+# --solutions--
+
+```js
+function getLongestChain(dominoes) {
+  function search(chain, remaining) {
+    let best = chain;
+    const last = chain[chain.length - 1][1];
+
+    for (let i = 0; i < remaining.length; i++) {
+      const [a, b] = remaining[i];
+      const rest = remaining.filter((_, j) => j !== i);
+
+      if (a === last) {
+        const result = search([...chain, [a, b]], rest);
+        if (result.length > best.length) best = result;
+      }
+      if (b === last && a !== b) {
+        const result = search([...chain, [b, a]], rest);
+        if (result.length > best.length) best = result;
+      }
+    }
+    return best;
+  }
+
+  let best = [];
+  for (let i = 0; i < dominoes.length; i++) {
+    const [a, b] = dominoes[i];
+    const rest = dominoes.filter((_, j) => j !== i);
+
+    const r1 = search([[a, b]], rest);
+    if (r1.length > best.length) best = r1;
+
+    if (a !== b) {
+      const r2 = search([[b, a]], rest);
+      if (r2.length > best.length) best = r2;
+    }
+  }
+  return best;
+}
+```

curriculum/challenges/english/blocks/daily-coding-challenges-javascript/69f35a5bb823ed620fcb7cb9.md

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+---
+id: 69f35a5bb823ed620fcb7cb9
+title: "Challenge 280: Mongo ID Date"
+challengeType: 28
+dashedName: challenge-280
+---
+
+# --description--
+
+Given a MongoDB ID string, return its creation time as an ISO 8601 string.
+
+- A MongoDB ID is a 24-character hex string. The first 8 characters represent a Unix timestamp (in seconds) encoded as a base-16 integer.
+
+For example, `"6a094b50bcf86cd799439011"` has a timestamp of `"6a094b50"` in hex, which is `1778994000` in decimal, representing a creation time of `"2026-05-17T05:00:00.000Z"`.
+
+# --hints--
+
+`mongoIdToDate("6a094b50bcf86cd799439011")` should return `"2026-05-17T05:00:00.000Z"`.
+
+```js
+assert.equal(mongoIdToDate("6a094b50bcf86cd799439011"), "2026-05-17T05:00:00.000Z");
+```
+
+`mongoIdToDate("695344eb1f4a4c1123042128")` should return `"2025-12-30T03:20:11.000Z"`.
+
+```js
+assert.equal(mongoIdToDate("695344eb1f4a4c1123042128"), "2025-12-30T03:20:11.000Z");
+```
+
+`mongoIdToDate("386da62df34123ac54617e56")` should return `"2000-01-01T07:01:01.000Z"`.
+
+```js
+assert.equal(mongoIdToDate("386da62df34123ac54617e56"), "2000-01-01T07:01:01.000Z");
+```
+
+`mongoIdToDate("69f571c3d7711807afd3dd55")` should return `"2026-05-02T03:38:43.000Z"`.
+
+```js
+assert.equal(mongoIdToDate("69f571c3d7711807afd3dd55"), "2026-05-02T03:38:43.000Z");
+```
+
+`mongoIdToDate("68adce01c0e1144d0a90295a")` should return `"2025-08-26T15:08:49.000Z"`.
+
+```js
+assert.equal(mongoIdToDate("68adce01c0e1144d0a90295a"), "2025-08-26T15:08:49.000Z");
+```
+
+# --seed--
+
+## --seed-contents--
+
+```js
+function mongoIdToDate(id) {
+
+  return id;
+}
+```
+
+# --solutions--
+
+```js
+function mongoIdToDate(id) {
+  const timestamp = parseInt(id.slice(0, 8), 16);
+  return new Date(timestamp * 1000).toISOString();
+}
+```

curriculum/challenges/english/blocks/daily-coding-challenges-javascript/69f35a5bb823ed620fcb7cba.md

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+---
+id: 69f35a5bb823ed620fcb7cba
+title: "Challenge 281: Bingo Range"
+challengeType: 28
+dashedName: challenge-281
+---
+
+# --description--
+
+Given a bingo letter, return the number range associated with that letter.
+
+| Letter | Number Range |
+| - | - |
+| `"B"` | 1-15 |
+| `"I"` | 16-30 |
+| `"N"` | 31-45 |
+| `"G"` | 46-60 |
+| `"O"` | 61-75 |
+
+Return an array with all numbers in the range from smallest to largest.
+
+# --hints--
+
+`getBingoRange("B")` should return `[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]`.
+
+```js
+assert.deepEqual(getBingoRange("B"), [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]);
+```
+
+`getBingoRange("I")` should return `[16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30]`.
+
+```js
+assert.deepEqual(getBingoRange("I"), [16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30]);
+```
+
+`getBingoRange("N")` should return `[31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45]`.
+
+```js
+assert.deepEqual(getBingoRange("N"), [31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45]);
+```
+
+`getBingoRange("G")` should return `[46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60]`.
+
+```js
+assert.deepEqual(getBingoRange("G"), [46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60]);
+```
+
+`getBingoRange("O")` should return `[61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75]`.
+
+```js
+assert.deepEqual(getBingoRange("O"), [61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75]);
+```
+
+# --seed--
+
+## --seed-contents--
+
+```js
+function getBingoRange(letter) {
+
+  return letter;
+}
+```
+
+# --solutions--
+
+```js
+function getBingoRange(letter) {
+  const ranges = { B: [1, 15], I: [16, 30], N: [31, 45], G: [46, 60], O: [61, 75] };
+  const [start, end] = ranges[letter];
+  return Array.from({ length: end - start + 1 }, (_, i) => start + i);
+}
+```

curriculum/challenges/english/blocks/daily-coding-challenges-javascript/69f35a5bb823ed620fcb7cbb.md

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+---
+id: 69f35a5bb823ed620fcb7cbb
+title: "Challenge 282: Sleep Debt"
+challengeType: 28
+dashedName: challenge-282
+---
+
+# --description--
+
+Given an array of hours slept each night leading up to today, and a target number of hours per night, return how many hours of sleep you need tonight to eliminate your sleep debt.
+
+- Include tonight's hours in the total time needed to catch up.
+- If you've slept enough to cover tonight's target or more, return `0`.
+
+# --hints--
+
+`sleepDebt([6, 6, 6, 6, 6, 6], 8)` should return `20`.
+
+```js
+assert.equal(sleepDebt([6, 6, 6, 6, 6, 6], 8), 20);
+```
+
+`sleepDebt([6, 7, 8, 4, 8, 6], 7)` should return `10`.
+
+```js
+assert.equal(sleepDebt([6, 7, 8, 4, 8, 6], 7), 10);
+```
+
+`sleepDebt([10, 10, 9, 10, 9, 11], 9)` should return `4`.
+
+```js
+assert.equal(sleepDebt([10, 10, 9, 10, 9, 11], 9), 4);
+```
+
+`sleepDebt([8, 7, 6, 7, 6, 8], 6)` should return `0`.
+
+```js
+assert.equal(sleepDebt([8, 7, 6, 7, 6, 8], 6), 0);
+```
+
+`sleepDebt([8, 9, 10, 9, 10, 7], 7)` should return `0`.
+
+```js
+assert.equal(sleepDebt([8, 9, 10, 9, 10, 7], 7), 0);
+```
+
+# --seed--
+
+## --seed-contents--
+
+```js
+function sleepDebt(hoursSlept, targetHours) {
+
+  return hoursSlept;
+}
+```
+
+# --solutions--
+
+```js
+function sleepDebt(hoursSlept, targetHours) {
+  const debt = (hoursSlept.length + 1) * targetHours - hoursSlept.reduce((sum, h) => sum + h, 0);
+  return Math.max(0, debt);
+}
+```

curriculum/challenges/english/blocks/daily-coding-challenges-javascript/69f35a5bb823ed620fcb7cbc.md

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+---
+id: 69f35a5bb823ed620fcb7cbc
+title: "Challenge 283: String Zipper"
+challengeType: 28
+dashedName: challenge-283
+---
+
+# --description--
+
+Given two strings, return a new string that interleaves their characters one at a time. If one string is longer, append the remaining characters at the end.
+
+Begin with the first character of the first string.
+
+# --hints--
+
+`zipStrings("abc", "123")` should return `"a1b2c3"`.
+
+```js
+assert.equal(zipStrings("abc", "123"), "a1b2c3");
+```
+
+`zipStrings("acegikmoqsuwy", "bdfhjlnprtvxz")` should return `"abcdefghijklmnopqrstuvwxyz"`.
+
+```js
+assert.equal(zipStrings("acegikmoqsuwy", "bdfhjlnprtvxz"), "abcdefghijklmnopqrstuvwxyz");
+```
+
+`zipStrings("day", "night")` should return `"dnaiyght"`.
+
+```js
+assert.equal(zipStrings("day", "night"), "dnaiyght");
+```
+
+`zipStrings("python", "javascript")` should return `"pjyatvhaosncript"`.
+
+```js
+assert.equal(zipStrings("python", "javascript"), "pjyatvhaosncript");
+```
+
+`zipStrings("feCdCm", "reoeap")` should return `"freeCodeCamp"`.
+
+```js
+assert.equal(zipStrings("feCdCm", "reoeap"), "freeCodeCamp");
+```
+
+# --seed--
+
+## --seed-contents--
+
+```js
+function zipStrings(a, b) {
+
+  return a;
+}
+```
+
+# --solutions--
+
+```js
+function zipStrings(a, b) {
+  let result = '';
+  const len = Math.max(a.length, b.length);
+  for (let i = 0; i < len; i++) {
+    if (i < a.length) result += a[i];
+    if (i < b.length) result += b[i];
+  }
+  return result;
+}
+```