added Backtracking/AllCombinationsOfSizeK

Author: chiranjeev-thapliyal

Backtracking/AllCombinationsOfSizeK.js

@@ -0,0 +1,57 @@
+/*
+  Problem: Given two numbers, n and k, make all unique combinations of k numbers from 1 to n and in sorted order
+
+  What is combinations?
+  - Combinations is selecting items froms a collections without considering order of selection
+
+  Example:
+  - We have an apple, a banana, and a jackfruit
+  - We have three objects, and need to choose two items, then combinations will be
+
+  1. Apple & Banana
+  2. Apple & Jackfruit
+  3. Banana & Jackfruit
+
+  To read more about combinations, you can visit the following link:
+  - https://betterexplained.com/articles/easy-permutations-and-combinations/
+
+  Solution:
+  - We will be using backtracking to solve this questions
+  - Take one element, and make all them combinations for k-1 elements
+  - Once we get all combinations of that element, pop it and do same for next element
+*/
+
+class Combinations {
+  constructor (n, k) {
+    this.n = n
+    this.k = k
+    this.combinationArray = [] // will be used for storing current combination
+  }
+
+  findCombinations (high = this.n, total = this.k, low = 1) {
+    if (total === 0) {
+      console.log(this.combinationArray)
+      return
+    }
+    for (let i = low; i <= high; i++) {
+      this.combinationArray.push(i)
+      this.findCombinations(high, total - 1, i + 1)
+      this.combinationArray.pop()
+    }
+  };
+}
+
+/*
+  Driver Code
+
+  Test Case 1: n = 3, k = 2
+  Test Case 2: n = 4, k = 2
+*/
+
+console.log('\nFirst Test Case')
+const test1 = new Combinations(3, 2)
+test1.findCombinations()
+
+console.log('\nSecond Test Case')
+const test2 = new Combinations(4, 2)
+test2.findCombinations()