Added JS solution for problem 40

Author: imaginate

javascript/40-Combination-Sum-II.js

@@ -0,0 +1,50 @@
+//////////////////////////////////////////////////////////////////////////////
+// Backtracking
+// Time: Theta(2^log(n)) O(2^n)
+// Space: Theta(2^log(n)) O(2^n)
+//////////////////////////////////////////////////////////////////////////////
+
+/**
+ * @param {number[]} candidates
+ * @param {number} target
+ * @return {number[][]}
+ */
+function combinationSum2(candidates, target) {
+    
+    candidates.sort((a, b) => a - b);
+    
+    const combos = [];
+    const combo = [];
+    const map = Object.create(null);
+    
+    for (let i = 0; i < candidates.length; ++i) {
+        map[candidates[i]] = i;
+    }
+    
+    getCombos(target);
+    return combos;
+    
+    /**
+     * @param {number} target
+     * @param {number=} start = `0`
+     * @return {void}
+     */
+    function getCombos(target, start = 0) {
+        
+        if (target in map && start <= map[target]) {
+            combo.push(target);
+            combos.push(combo.slice());
+            combo.pop();
+        }
+        
+        const mid = Math.floor(target / 2);
+        for (let i = start; i < candidates.length && candidates[i] <= mid; ++i) {
+            if (i !== start && candidates[i] === candidates[i - 1]) {
+                continue;
+            }
+            combo.push(candidates[i]);
+            getCombos(target - candidates[i], i + 1);
+            combo.pop();
+        }
+    }
+}