[LeetCode]Permutations

Permutations

Given a collection of 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], and [3,2,1].

 

递归实现，回溯。这是一类题目。

遍历所有可能,符合条件放入结果中。

class Solution {
public:
    void dfs(int length,vector<int> nums,vector<vector<int>>& result)
    {
        if(length==nums.size())
        {
            result.push_back(nums);
            return;
        }
        for(int i=length;i<nums.size();i++)
        {
            swap(nums[length],nums[i]);
            dfs(length+1,nums,result);
            swap(nums[length],nums[i]);
        }
    }
    vector<vector<int>> permute(vector<int>& nums) {
        vector<vector<int>> result;
        dfs(0,nums,result);
        return result;
    }
};