permutation question

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// Your code here
 
class Solution {
public:
    vector<vector<int>> ans;
    vector<int> path;
    vector<bool> used;
 
    void solve(vector<int>& nums) {
 
        // Base Case
        // One complete permutation formed
        if(path.size() == nums.size()) {
            ans.push_back(path);
            return;
        }
 
        // for(each choice)
        for(int i = 0; i < nums.size(); i++) {
 
            // Skip if already chosen
            if(used[i])
                continue;
 
            // ------------------
            // CHOOSE
            // ------------------
            path.push_back(nums[i]);
            used[i] = true;
 
            // Example:
            // [] -> [1]
            // [1] -> [1,2]
 
            // ------------------
            // SOLVE
            // ------------------
            solve(nums);
 
            // Explore everything
            // possible after choosing nums[i]
 
            // ------------------
            // UNDO
            // ------------------
            path.pop_back();
            used[i] = false;
 
            // Restore state
            // [1,2] -> [1]
            // [1] -> []
        }
    }
 
    vector<vector<int>> permute(vector<int>& nums) {
 
        used.resize(nums.size(), false);
 
        solve(nums);
 
        return ans;
    }
};