Added combinationSum solution

Author: nhistory

combination-sum/nhistory.js

@@ -0,0 +1,26 @@
+var combinationSum = function (candidates, target) {
+  let output = [];
+
+  // Helper function for depth-first search
+  const dfs = (index, currentVal, arr) => {
+    // If the remaining value is less than 0, no need to proceed further
+    if (currentVal < 0) return;
+    // If we have found a valid combination
+    if (currentVal === 0) {
+      output.push([...arr]);
+      return;
+    }
+
+    // Iterate over the candidates starting from the current index
+    for (let i = index; i < candidates.length; i++) {
+      arr.push(candidates[i]);
+      dfs(i, currentVal - candidates[i], arr);
+      arr.pop(); // backtrack
+    }
+  };
+
+  // Start DFS with the initial target and empty combination
+  dfs(0, target, []);
+
+  return output;
+};