Create countPairs.js

Author: Defite

countPairs.js

@@ -0,0 +1,25 @@
+/**
+* This also called 'Sock Merchant' or 'Count duplicates in array'
+*/
+
+var data = [10, 20, 20, 10, 10, 30, 50, 10, 20, 50];
+
+function countPairs(arr) {
+  var counter = 0;
+  
+  // Sort array
+  arr.sort(function(a, b) {
+    return a - b;
+  });
+  
+  for (var i = 0; i < data.length - 1; i++) {
+    if (arr[i] === arr[i+1]) {
+      counter++;
+      i++;
+    }
+  }
+  
+  return counter; // 3
+}
+
+countPairs(data); // 3