diff --git a/sum-of-pairs/index.js b/sum-of-pairs/index.js
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+++ b/sum-of-pairs/index.js
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+// https://www.codewars.com/kata/sum-of-pairs/train/javascript
+
+const sum_pairs = (arr, sum) => {
+  const map = new WeakMap();
+  for (let i = 0; i < arr.length; ++i) {
+    if (map[arr[i]]) {
+      return [sum - arr[i], arr[i]];
+    }
+    map[sum - arr[i]] = true;
+  }
+  return [];
+};