Permutations

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Problem

Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order.

Example 1:

Input: nums = [1,2,3]
Output: [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]

Example 2:

Input: nums = [0,1]
Output: [[0,1],[1,0]]

Example 3:

Input: nums = [1]
Output: [[1]]

Pseudocode

- dfs with a for loop within
    - permutation with backtracking
    
- same as combination sum, don't understand this intuitively

Solution

// from solutions
// https://leetcode.com/problems/permutations/solutions/685868/dfs-backtracking-python-java-javascript-picture/
// good illustration on how to approach the problem
// time O(N^N), has to find every permutation
var permute = function (nums) {
  let res = [];
  dfs(nums, [], Array(nums.length).fill(false), res);
  return res;
};

function dfs(nums, path, used, res) {
  // console.log(path)
  if (path.length == nums.length) {
    // make a deep copy since otherwise we'd be append the same list over and over
    res.push(Array.from(path));
    return;
  }
  for (let i = 0; i < nums.length; i++) {
    // skip used nums
    if (used[i]) continue;
    // add letter to permutation, mark letter as used
    path.push(nums[i]);
    used[i] = true;
    dfs(nums, path, used, res);
    // remove letter from permutation, mark letter as unused
    path.pop();
    used[i] = false;
  }
}

Time and Space Complexity

Time

• What did the code do

• Total -

Space

• What did the code do

• Total -