46. Permutations

https://leetcode.com/problems/permutations/

Problem

Given a collection of distinct integers, return all possible permutations.

Example:

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

Solution

class Solution {
public:
    vector<vector<int>> permute(vector<int>& nums) {
        vector<vector<int>> per;
        if (nums.empty()) return per;
        permute(per, nums, 0);
        return per;
    }
    void permute(vector<vector<int>> &per, vector<int>& nums, int index) {
        if (nums.size() - 1 == index) return per.push_back(nums);
        for (int i = index; i < nums.size(); ++i) {
            swap(nums[index], nums[i]);
            permute(per, nums, index + 1);
            swap(nums[index], nums[i]);
        }
    }
    inline void swap(int &a, int &b){
        int temp = a;
        a = b;
        b = temp;
    }
};

• #dfs