46. Permutations

题目

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

For example,
[1,2,3] have the following permutations:

[
  [1,2,3],
  [1,3,2],
  [2,1,3],
  [2,3,1],
  [3,1,2],
  [3,2,1]
]

解析

class Solution_46 {
public:
    void help(int i,vector<int> &nums,vector<vector<int>> &vecs)
    {
        
        if (i==nums.size())
        {
            vecs.push_back(nums);
            return;
        }
        else
        {
            for (int j = i; j < nums.size();j++)
            {
                swap(nums[i],nums[j]);
                help(i + 1, nums,vecs);
                swap(nums[i],nums[j]);
            }
        }
        return;
    }

    vector<vector<int>> permute(vector<int>& nums) {

        vector<vector<int>> vecs;

        if (nums.size()==0)
        {
            return vecs;
        }

        help(0, nums,vecs);

        return vecs;
    }
};

题目来源

• 46. Permutations 排列数