diff --git a/README.md b/README.md
index 36e5f15..d39c9b4 100644
--- a/README.md
+++ b/README.md
@@ -27,6 +27,18 @@
| Solution |
Topics |
+
+ | September 12th |
+ 2006. Count Number of Pairs With Absolute Difference K |
+ $\text{\color{TealBlue}Easy}$ |
+
+ Hash Table
+ |
+
+ Array,
+ Hash Table
+ |
+
| September 11th |
2006. Count Number of Pairs With Absolute Difference K |
@@ -74,17 +86,6 @@
Dynamic Programming
-
- | September 7th |
- 1155. Number of Dice Rolls With Target Sum |
- $\text{\color{Dandelion}Medium}$ |
-
- Dynamic Programming - Tabulation
- |
-
- Dynamic Programming
- |
-
@@ -1565,13 +1566,15 @@
2006 |
Count Number of Pairs With Absolute Difference K |
Java with
- Brute Force or
- Counting
+ Brute Force,
+ Counting or
+ Hash Table
|
$\text{\color{TealBlue}Easy}$ |
Array,
- Counting
+ Counting,
+ Hash Table
|
|
@@ -3383,10 +3386,12 @@
$\text{\color{TealBlue}Easy}$ |
Array,
- Counting
+ Counting,
+ Hash Table
|
Solution Using
- Brute Force Approach
+ Brute Force Approach or
+ Hash Table
|
@@ -5554,6 +5559,23 @@
|
+
+ | 2006 |
+ Count Number of Pairs With Absolute Difference K |
+
+ Java
+ |
+ $\text{\color{TealBlue}Easy}$ |
+
+ Array,
+ Counting,
+ Hash Table
+ |
+ Solution Using
+ Brute Force,
+ Counting
+ |
+
| 2007 |
Find Original Array From Doubled Array |
diff --git a/solutions/2006. Count Number of Pairs With Absolute Difference K/CountNumberOfPairsWithAbsoluteDifferenceK_HashTable.java b/solutions/2006. Count Number of Pairs With Absolute Difference K/CountNumberOfPairsWithAbsoluteDifferenceK_HashTable.java
new file mode 100644
index 0000000..5e86fae
--- /dev/null
+++ b/solutions/2006. Count Number of Pairs With Absolute Difference K/CountNumberOfPairsWithAbsoluteDifferenceK_HashTable.java
@@ -0,0 +1,46 @@
+package com.cheehwatang.leetcode;
+
+import java.util.HashMap;
+import java.util.Map;
+
+// Time Complexity : O(n),
+// where 'n' is the length of 'nums'.
+// We traverse 'nums' to count the numbers in 'nums', and we traverse the HashMap with a maximum size of 'n'.
+//
+// Space Complexity : O(n),
+// where 'n' is the length of 'nums'.
+// The HashMap has a maximum size of 'n' if the numbers in 'nums' are all unique.
+
+public class CountNumberOfPairsWithAbsoluteDifferenceK_HashTable {
+
+ // Approach:
+ // Using a HashMap to record the frequency of occurrence for all the numbers in 'nums'.
+ // This only add the number to the HashMap if it is in 'nums'.
+
+ public int countKDifference(int[] nums, int k) {
+
+ // Record the frequency for all the numbers into the HashMap.
+ Map map = new HashMap<>();
+ for (int number : nums) {
+ map.put(number, map.getOrDefault(number, 0) + 1);
+ }
+
+ // The number of combinations is the multiples of both frequency.
+ // e.g. [1,1,2,2,2] can have 2 * 3 = 6 combinations for k = 1.
+ // Check for the frequency for both key - k and key + k, as the k difference can be in both directions.
+ // Once the count is added, set the value of the number in the HashMap to 0, so that it will not be double counted.
+ // Do note that we cannot remove the key-value pair,
+ // as it causes Exceptions in the map.keySet() which uses an iterator.
+ int count = 0;
+ for (Integer key : map.keySet()) {
+ if (map.containsKey(key - k)) {
+ count += map.get(key) * map.get(key - k);
+ }
+ if (map.containsKey(key + k)) {
+ count += map.get(key) * map.get(key + k);
+ }
+ map.put(key, 0);
+ }
+ return count;
+ }
+}