edit 216

Author: fishercoder1534

README.md

@@ -358,6 +358,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |219|[Contains Duplicate II](https://leetcode.com/problems/contains-duplicate-ii/)|[Solution](../master/src/main/java/com/fishercoder/solutions/ContainsDuplicateII.java)| O(n)|O(n) | Easy| HashMap
 |218|[The Skyline Problem](https://leetcode.com/problems/the-skyline-problem/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_218.java)| O(n)|O(n) | Hard| TreeMap, Design
 |217|[Contains Duplicate](https://leetcode.com/problems/contains-duplicate/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_217.java)| O(n)|O(n) | Easy| HashSet
+|216|[Combination Sum III](https://leetcode.com/problems/combination-sum-iii/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_216.java)| O(k * C(n, k))|O(k) | Medium| Backtracking
 |215|[Kth Largest Element in an Array](https://leetcode.com/problems/kth-largest-element-in-an-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_215.java)| O(nlogn)|O(n) | Medium| Heap
 |214|[Shortest Palindrome](https://leetcode.com/problems/shortest-palindrome/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_214.java)| O(?)|O(?)| Hard | KMP
 |213|[House Robber II](https://leetcode.com/problems/house-robber-ii/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_213.java)| O(n)|O(n)| Medium | DP

src/main/java/com/fishercoder/solutions/CombinationSumIII.java renamed to src/main/java/com/fishercoder/solutions/_216.java

@@ -2,7 +2,10 @@
 
 import java.util.*;
 
-/**Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers.
+/**
+ * 216. Combination Sum III
+ * Find all possible combinations of k numbers that add up to a number n,
+ * given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers.
 
 
  Example 1:
@@ -20,7 +23,8 @@
  Output:
 
  [[1,2,6], [1,3,5], [2,3,4]]*/
-public class CombinationSumIII {
+public class _216 {
+
     public List<List<Integer>> combinationSum3(int k, int n) {
         List<List<Integer>> result = new ArrayList();
         int[] nums = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
@@ -32,11 +36,9 @@ void helper(int k, int n, int[] nums, int start, List<Integer> curr, List<List<I
         if (n > 0) {
             for (int i = start; i < nums.length; i++) {
                 curr.add(nums[i]);
-                helper(k, n - nums[i], nums, i + 1, curr, result);// it needs to be a unique set of
-                                                                  // numbers, so we need to set it
-                                                                  // as i+1 here: each number is
-                                                                  // used only once in this array:
-                                                                  // [1,2,3,4,5,6,7,8,9]
+                /** it needs to be a unique set of numbers, so we need to set it
+                 as i+1 here: each number is used only once in this array: [1,2,3,4,5,6,7,8,9]*/
+                helper(k, n - nums[i], nums, i + 1, curr, result);
                 curr.remove(curr.size() - 1);
             }
         } else if (n == 0 && curr.size() == k) {//this is the major difference here: check size of curr list is of k before adding it