1. Record node
Every node of the recursion tree is itself a valid subset.
result.push([...path])Typorithm · medium
Subsets
▷ Interactive algorithm labsubsetsbacktrackingpower-setchoose-explore-undostart-index
Saved on this device
Full lesson · 8 learning steps Open any exercise for focused practice
10%
Step 1 of 8 · intro card
Learn Subsets
Backtracking
Build the power set by recording every node of a choose / explore / undo recursion tree.
Every subset corresponds to a node in a recursion tree that grows by adding one later element at a time.
A start index ensures each element is only ever extended forward, so no subset repeats.
Push to choose, recurse to explore, then pop to undo — the universal backtracking shape.
Preparing algorithm lab…
01
Record the path at every node.
02
Loop from start to avoid duplicates.
03
Choose, recurse, then undo.
function subsets(nums) {
const result = [];
function backtrack(start, path) {
result.push([...path]);
for (let i = start; i < nums.length; i += 1) {
path.push(nums[i]);
backtrack(i + 1, path);
path.pop();
}
}
backtrack(0, []);
return result;
}Read the implementation
Connect each part of the code to the concept before you type.
2. Choices from start
Starting at start avoids reusing earlier elements and duplicate subsets.
for (let i = start; i < nums.length; i += 1)3. Choose
Add the current element to the path.
path.push(nums[i])4. Explore
Recurse with the next start so each element is used at most once.
backtrack(i + 1, path)5. Undo
Remove the element to restore state for the next choice.
path.pop()A complete learning loop
01
Understand
Read the concept map and follow the code breakdown.
02
Reconstruct
Type the implementation, repair mistakes and work through every recall exercise.
03
Verify
Use the final check without hints; revisit weak concepts in short practice sessions.