program-1/program1.cp at main · hhm14/program-1 · GitHub

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//page 33 exercise 2.14
class Solution {
public:
    vector<vector<int>> ans;
    vector<vector<int>> permute(vector<int>& nums) {
    int elements = nums.size(); // num elements given
    bookalgo(nums, elements, ans);
    return ans;
    }
    void bookalgo(vector<int>& nums, int elements, vector<vector<int>>& ans)
    {
        if(elements == 1) { //base case
            ans.push_back(nums);
        }
        else
        {
            bookalgo(nums, elements-1, ans); //recursive step, decrease + conquer
            for(int i = 0; i < elements-1; ++i)
            {
                if (elements %2 == 1) // odd
                {
                    swap(nums[0], nums[elements-1]);
                }
                else // even
                {
                    swap(nums[i], nums[elements-1]);
                }
                bookalgo(nums, elements-1, ans); //decreasing size again
            }
        }

    }
};