Add solution #1128

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,143 LeetCode solutions in JavaScript
+# 1,144 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -889,6 +889,7 @@
 1123|[Lowest Common Ancestor of Deepest Leaves](./solutions/1123-lowest-common-ancestor-of-deepest-leaves.js)|Medium|
 1124|[Longest Well-Performing Interval](./solutions/1124-longest-well-performing-interval.js)|Medium|
 1125|[Smallest Sufficient Team](./solutions/1125-smallest-sufficient-team.js)|Hard|
+1128|[Number of Equivalent Domino Pairs](./solutions/1128-number-of-equivalent-domino-pairs.js)|Easy|
 1137|[N-th Tribonacci Number](./solutions/1137-n-th-tribonacci-number.js)|Easy|
 1143|[Longest Common Subsequence](./solutions/1143-longest-common-subsequence.js)|Medium|
 1161|[Maximum Level Sum of a Binary Tree](./solutions/1161-maximum-level-sum-of-a-binary-tree.js)|Medium|

solutions/1128-number-of-equivalent-domino-pairs.js

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+/**
+ * 1128. Number of Equivalent Domino Pairs
+ * https://leetcode.com/problems/number-of-equivalent-domino-pairs/
+ * Difficulty: Easy
+ *
+ * Given a list of dominoes, dominoes[i] = [a, b] is equivalent to dominoes[j] = [c, d]
+ * if and only if either (a == c and b == d), or (a == d and b == c) - that is, one domino
+ * can be rotated to be equal to another domino.
+ *
+ * Return the number of pairs (i, j) for which 0 <= i < j < dominoes.length, and
+ * dominoes[i] is equivalent to dominoes[j].
+ */
+
+/**
+ * @param {number[][]} dominoes
+ * @return {number}
+ */
+var numEquivDominoPairs = function(dominoes) {
+  const map = new Map();
+  let result = 0;
+
+  for (const [a, b] of dominoes) {
+    const key = Math.min(a, b) * 10 + Math.max(a, b);
+    const count = map.get(key) || 0;
+    result += count;
+    map.set(key, count + 1);
+  }
+
+  return result;
+};