feat: add Combination Sumsubsets

Author: dukeluo

README.md

@@ -73,6 +73,7 @@ Roadmap: https://neetcode.io/roadmap
 | 105  | [Construct Binary Tree from Preorder and Inorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/description/) | Medium     | [ts](./TypeScript/105.construct-binary-tree-from-preorder-and-inorder-traversal.ts)           | Trees            |
 | 46   | [Permutations](https://leetcode.com/problems/permutations/)                                                                                                       | Medium     | [ts](./TypeScript/46.permutations.ts)                                                         | Backtracking     |
 | 78   | [Subsets](https://leetcode.com/problems/subsets/description/)                                                                                                     | Medium     | [ts](./TypeScript/78.subsets.ts)                                                              | Backtracking     |
+| 39   | [Combination Sum](https://leetcode.com/problems/combination-sum/description/)                                                                                     | Medium     | [ts](./TypeScript/39.combination-sum.ts)                                                      | Backtracking     |
 
 ### Others
 

TypeScript/39.combination-sum.ts

@@ -0,0 +1,26 @@
+function combinationSum(candidates: number[], target: number): number[][] {
+  const combinations = [];
+
+  function dfs(i, combination, total) {
+    if (total === target) {
+      combinations.push(combination.slice());
+      return;
+    }
+
+    if (i >= candidates.length || total > target) {
+      return;
+    }
+
+    combination.push(candidates[i]);
+    dfs(i, combination, total + candidates[i]);
+
+    combination.pop();
+    dfs(i + 1, combination, total);
+  }
+
+  dfs(0, [], 0);
+
+  return combinations;
+}
+
+console.log(combinationSum([2, 3, 6, 7], 7));