Add solution #1942

JoshCrozier · JoshCrozier · commit 2003f8e5eb42 · 2025-07-25T00:16:38.000-05:00
diff --git a/README.md b/README.md
@@ -1763,6 +1763,7 @@
 1938|[Maximum Genetic Difference Query](./solutions/1938-maximum-genetic-difference-query.js)|Hard|
 1940|[Longest Common Subsequence Between Sorted Arrays](./solutions/1940-longest-common-subsequence-between-sorted-arrays.js)|Medium|
 1941|[Check if All Characters Have Equal Number of Occurrences](./solutions/1941-check-if-all-characters-have-equal-number-of-occurrences.js)|Easy|
+1942|[The Number of the Smallest Unoccupied Chair](./solutions/1942-the-number-of-the-smallest-unoccupied-chair.js)|Medium|
 1943|[Describe the Painting](./solutions/1943-describe-the-painting.js)|Medium|
 1944|[Number of Visible People in a Queue](./solutions/1944-number-of-visible-people-in-a-queue.js)|Hard|
 1945|[Sum of Digits of String After Convert](./solutions/1945-sum-of-digits-of-string-after-convert.js)|Easy|
diff --git a/solutions/1942-the-number-of-the-smallest-unoccupied-chair.js b/solutions/1942-the-number-of-the-smallest-unoccupied-chair.js
@@ -0,0 +1,62 @@
+/**
+ * 1942. The Number of the Smallest Unoccupied Chair
+ * https://leetcode.com/problems/the-number-of-the-smallest-unoccupied-chair/
+ * Difficulty: Medium
+ *
+ * There is a party where n friends numbered from 0 to n - 1 are attending. There is an infinite
+ * number of chairs in this party that are numbered from 0 to infinity. When a friend arrives at
+ * the party, they sit on the unoccupied chair with the smallest number.
+ * - For example, if chairs 0, 1, and 5 are occupied when a friend comes, they will sit on chair
+ *   number 2.
+ *
+ * When a friend leaves the party, their chair becomes unoccupied at the moment they leave.
+ * If another friend arrives at that same moment, they can sit in that chair.
+ *
+ * You are given a 0-indexed 2D integer array times where times[i] = [arrivali, leavingi],
+ * indicating the arrival and leaving times of the ith friend respectively, and an integer
+ * targetFriend. All arrival times are distinct.
+ *
+ * Return the chair number that the friend numbered targetFriend will sit on.
+ */
+
+/**
+ * @param {number[][]} times
+ * @param {number} targetFriend
+ * @return {number}
+ */
+var smallestChair = function(times, targetFriend) {
+  const events = [];
+
+  for (let i = 0; i < times.length; i++) {
+    events.push([times[i][0], 'arrive', i]);
+    events.push([times[i][1], 'leave', i]);
+  }
+
+  events.sort((a, b) => a[0] - b[0] || (a[1] === 'leave' ? -1 : 1));
+
+  const availableChairs = [];
+  const occupiedChairs = new Map();
+  let nextChair = 0;
+
+  for (const [time, eventType, friendId] of events) {
+    if (eventType === 'leave') {
+      const chairNumber = occupiedChairs.get(friendId);
+      occupiedChairs.delete(friendId);
+      availableChairs.push(chairNumber);
+      availableChairs.sort((a, b) => a - b);
+    } else {
+      let assignedChair;
+      if (availableChairs.length > 0) {
+        assignedChair = availableChairs.shift();
+      } else {
+        assignedChair = nextChair++;
+      }
+
+      occupiedChairs.set(friendId, assignedChair);
+
+      if (friendId === targetFriend) {
+        return assignedChair;
+      }
+    }
+  }
+};
