Add solution #1583

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,383 LeetCode solutions in JavaScript
+# 1,384 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -1208,6 +1208,7 @@
 1578|[Minimum Time to Make Rope Colorful](./solutions/1578-minimum-time-to-make-rope-colorful.js)|Medium|
 1579|[Remove Max Number of Edges to Keep Graph Fully Traversable](./solutions/1579-remove-max-number-of-edges-to-keep-graph-fully-traversable.js)|Hard|
 1582|[Special Positions in a Binary Matrix](./solutions/1582-special-positions-in-a-binary-matrix.js)|Easy|
+1583|[Count Unhappy Friends](./solutions/1583-count-unhappy-friends.js)|Medium|
 1598|[Crawler Log Folder](./solutions/1598-crawler-log-folder.js)|Easy|
 1657|[Determine if Two Strings Are Close](./solutions/1657-determine-if-two-strings-are-close.js)|Medium|
 1668|[Maximum Repeating Substring](./solutions/1668-maximum-repeating-substring.js)|Easy|

solutions/1583-count-unhappy-friends.js

@@ -0,0 +1,58 @@
+/**
+ * 1583. Count Unhappy Friends
+ * https://leetcode.com/problems/count-unhappy-friends/
+ * Difficulty: Medium
+ *
+ * You are given a list of preferences for n friends, where n is always even.
+ *
+ * For each person i, preferences[i] contains a list of friends sorted in the order of preference.
+ * In other words, a friend earlier in the list is more preferred than a friend later in the list.
+ * Friends in each list are denoted by integers from 0 to n-1.
+ *
+ * All the friends are divided into pairs. The pairings are given in a list pairs, where
+ * pairs[i] = [xi, yi] denotes xi is paired with yi and yi is paired with xi.
+ *
+ * However, this pairing may cause some of the friends to be unhappy. A friend x is unhappy if x
+ * is paired with y and there exists a friend u who is paired with v but:
+ * - x prefers u over y, and
+ * - u prefers x over v.
+ *
+ * Return the number of unhappy friends.
+ */
+
+/**
+ * @param {number} n
+ * @param {number[][]} preferences
+ * @param {number[][]} pairs
+ * @return {number}
+ */
+var unhappyFriends = function(n, preferences, pairs) {
+  const rank = Array.from({ length: n }, () => new Array(n).fill(0));
+  const pairMap = new Array(n).fill(0);
+  let result = 0;
+
+  for (let i = 0; i < n; i++) {
+    for (let j = 0; j < n - 1; j++) {
+      rank[i][preferences[i][j]] = j;
+    }
+  }
+
+  for (const [x, y] of pairs) {
+    pairMap[x] = y;
+    pairMap[y] = x;
+  }
+
+  for (let x = 0; x < n; x++) {
+    const y = pairMap[x];
+    for (const u of preferences[x]) {
+      if (u === y) break;
+      const v = pairMap[u];
+      if (rank[u][x] < rank[u][v]) {
+        result++;
+        break;
+      }
+    }
+  }
+
+  return result;
+};