LeetCode #46: Permutations (C/C++).

medium

source: https://leetcode.com/problems/permutations/
C/C++ Solution to LeetCode problem 46. Permutations.

Problem

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

Examples

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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]]

Constraints

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• 1 <= nums.length <= 6
• -10 <= nums[i] <= 10
• All the integers of nums are unique.

Solution

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This can be solved using Backtracking (see more backtracking problems)

class Solution {
private:
  vector<vector<int>> result;

  void permutations(vector<int>& nums, int index) {
    if (index == nums.size()) {
      result.push_back(nums);
      return;
    }

    for (int i=index; i<nums.size(); i++) {
      swap(nums[index], nums[i]);
      permutations(nums, index+1);
      swap(nums[index], nums[i]);
    }
  }
public:
  vector<vector<int>> permute(vector<int>& nums) {
    permutations(nums, 0);

    return result;
  }
};