Backtracking

// C++ Program to Array Permutations
#include <iostream>
#include <vector>
#include <algorithm>

void solve(std::vector<int>& nums, int index, std::vector<std::vector<int>>& ans) {
    // If index is equal to size of num then store our num vector in ans and return 
    if(index >= nums.size()) {
        ans.push_back(nums);
        return;
    }

    // Looping from index till size of the array
    for(int i = index; i < nums.size(); i++) {
        // Swap the ind and ith numbers in nums array
        std::swap(nums[index], nums[i]);
        // Recursive Call with increase in the index
        solve(nums, index + 1, ans);
        // backtracking
        std::swap(nums[index], nums[i]);
    }
}

std::vector<std::vector<int>> arrayPermutations(std::vector<int>& nums) {
    // Initializing answer vector where we store permutations
    std::vector<std::vector<int>> ans;
    int index = 0;   // index of the starting point
    
    // Function Call 
    solve(nums, index, ans);
    
    return ans;
}

int main() {
    // Initializing array
    std::vector<int> arr = {1, 2, 3, 4};
    
    // Function Call
    std::vector<std::vector<int>> permutations = arrayPermutations(arr);
    // Printing the permutations of vector arr
    std::cout << "Permutations of {1, 2, 3, 4} are: " << std::endl;
    for(int i = 0; i < permutations.size(); i++) {
        std::cout << " [ ";
        for(int j = 0; j < permutations[i].size(); j++) {
            std::cout << permutations[i][j] << " ";
        }
        if(i != permutations.size() - 1) std::cout << "] ,";
    }
    std::cout << "]";
    return 0;
}