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codereview/pairDifferenceCounter.md

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+## Problem
+
+Adapted from [this HackerRank Problem](https://www.hackerrank.com/challenges/pairs/problem).
+
+> Given `N` integers, count the number of pairs of integers whose difference is `K`.
+
+## Approach
+
+1. Given the initial `int` array, sort it.
+2. Now iterate through the indices in the array using a lower index (starting at `0`) and an upper index (starting at `1`)`.
+3. Calculate the difference between the value at the upper index value and the value at the lower index
+  a. If the difference is equal to the target difference, increment the count and increment the upper index.
+  b. If the difference is less than the target difference, increment the upper index. A difference less than the target
+     difference implies that the value at the upper index is not large enough.
+  c. If the difference is greater than the target difference, increment the lower index. A difference greater than the
+     target implies that the value at the lower index is not large enough.
+4. Return the count
+
+## Implementation
+
+<!--language: lang-java -->
+
+    public class PairDifferenceCounter {
+        public static int countPairsWithDifference(int[] values, int difference) {
+            Arrays.sort(values);
+
+            int count = 0;
+            int lowerIndex = 0;
+            int upperIndex = 1;
+
+            while (upperIndex < values.length) {
+                int pairDifference = values[upperIndex] - values[lowerIndex];
+
+                if (pairDifference == difference) {
+                    count++;
+                    upperIndex++;
+                } else if (pairDifference > difference) {
+                    lowerIndex++;
+                } else {
+                    upperIndex++;
+                }
+            }
+
+            return count;
+        }
+    }