Leetcode 46

Permutations

• Problem Description：
  經典回溯問題：無重複數字的全排列
  具體的題目資訊：
  https://leetcode.com/problems/permutations/description/
• Example:
  
• Solution:

class Solution {
public:
    vector<vector<int>> permute(vector<int>& nums) {
        vector<vector<int
 
>> res;
        if (nums.size() == 0) return res;
        permutation(nums, 0, res);
        return res;
    }
    void permutation(vector<int>& nums, int i, vector<vector<int>>& res) {
        if (i == nums.size()-1) {
            vector<int> t;
            for (int
 
 j = 0; j < nums.size(); j++) {
                t.push_back(nums[j]);
            }
            res.push_back(t);
            return;
        } else {
            for (int j = i; j < nums.size(); j++) {
                swap(nums, i, j);
                permutation(nums, i+1, res);
                swap(nums, j, i);
            }
        }
    }
    void
 
 swap(vector<int>& nums, int i, int j) {
        int t = nums[i];
        nums[i] = nums[j];
        nums[j] = t;
    }
};