Add solution #40

Author: JoshCrozier

README.md

@@ -40,6 +40,7 @@
 35|[Search Insert Position](./0035-search-insert-position.js)|Easy|
 36|[Valid Sudoku](./0036-valid-sudoku.js)|Medium|
 39|[Combination Sum](./0039-combination-sum.js)|Medium|
+40|[Combination Sum II](./0040-combination-sum-ii.js)|Medium|
 41|[First Missing Positive](./0041-first-missing-positive.js)|Hard|
 42|[Trapping Rain Water](./0042-trapping-rain-water.js)|Hard|
 43|[Multiply Strings](./0043-multiply-strings.js)|Medium|

solutions/0040-combination-sum-ii.js

@@ -0,0 +1,37 @@
+/**
+ * 40. Combination Sum II
+ * https://leetcode.com/problems/combination-sum-ii/
+ * Difficulty: Medium
+ *
+ * Given a collection of candidate numbers (candidates) and a target number (target),
+ * find all unique combinations in candidates where the candidate numbers sum to target.
+ *
+ * Each number in candidates may only be used once in the combination.
+ *
+ * Note: The solution set must not contain duplicate combinations.
+ */
+
+/**
+ * @param {number[]} candidates
+ * @param {number} target
+ * @return {number[][]}
+ */
+var combinationSum2 = function(candidates, target) {
+  const result = [];
+  candidates.sort((a, b) => a - b);
+  backtrack(result, candidates, target);
+  return result;
+};
+
+function backtrack(result, candidates, target, combination = [], offset = 0) {
+  if (target < 0) {
+    return;
+  } else if (target === 0) {
+    result.push(combination);
+  } else {
+    for (let i = offset; i < candidates.length; i++) {
+      if (i > offset && candidates[i] === candidates[i - 1]) continue;
+      backtrack(result, candidates, target - candidates[i], [...combination, candidates[i]], i + 1);
+    }
+  }
+}