1 #include "000库函数.h"
2
3
4 //使用排序，感觉在作弊，但是题目没说不可以
5 //24ms
6 class solution {
7 public:
8 vector<vector<int>> permute(vector<int>& nums) {
9 vector<vector<int>>res;
10 if (nums.empty())return res;
11 sort(nums.begin(), nums.end());//排序
12 do {
13 res.push_back(nums);
14 } while (next_permutation(nums.begin(), nums.end()));
15 return res;
16 }
17 };
18
19 //使用递归
20 class Solution {
21 public:
22 vector<vector<int>> permute(vector<int>& nums) {
23 vector<vector<int>>Res;
24 if (nums.empty())return Res;
25 Combin(Res, nums, 0);//回溯
26 return Res;
27 }
28 void Combin(vector<vector<int>>&Res, vector<int>v, int s) {
29 if (s >= v.size()) //此处不return，在for中结束后自动结束
30 Res.push_back(v);
31
32 for (int i = s; i < v.size(); ++i) {
33 swap(v[s], v[i]);//交换
34 Combin(Res, v, s + 1);//回溯
35 swap(v[s], v[i]);//换回来
36 }
37 }
38
39 };
40
41 ////使用DFS递归
42 class Solution {
43 public:
44 vector<vector<int>> permute(vector<int>& num) {
45 vector<vector<int>> res;
46 vector<int> out, visited(num.size(), 0);
47 permuteDFS(num, 0, visited, out, res);
48 return res;
49 }
50 void permuteDFS(vector<int>& num, int level, vector<int>& visited, vector<int>& out, vector<vector<int>>& res) {
51 if (level == num.size()) { res.push_back(out); return; }//数字大小达到要求
52 for (int i = 0; i < num.size(); ++i) {
53 if (visited[i] == 1) continue;
54 visited[i] = 1;//该数据已经选用
55 out.push_back(num[i]);
56 permuteDFS(num, level + 1, visited, out, res);
57 out.pop_back();//回溯
58 visited[i] = 0;
59 }
60 }
61 };
62
63 //当n = 1时，数组中只有一个数a1，其全排列只有一种，即为a1
64 //
65 //当n = 2时，数组中此时有a1a2，其全排列有两种，a1a2和a2a1，那么此时我们考虑和上面那种情况的关系，我们发现，其实就是在a1的前后两个位置分别加入了a2
66 //
67 //当n = 3时，数组中有a1a2a3，此时全排列有六种，分别为a1a2a3, a1a3a2, a2a1a3, a2a3a1, a3a1a2, 和 a3a2a1。那么根据上面的结论，实际上是在a1a2和a2a1的基础上在不同的位置上加入a3而得到的。
68 //
69 //_ a1 _ a2 _ : a3a1a2, a1a3a2, a1a2a3
70 //
71 //_ a2 _ a1 _ : a3a2a1, a2a3a1, a2a1a3
72 class Solution {
73 public:
74 vector<vector<int>> permute(vector<int>& num) {
75 vector<vector<int>> res;
76 if (num.empty()) return res;
77 int first = num[0];
78 num.erase(num.begin());//删除此数字
79 vector<vector<int>> words = permute(num);
80 for (auto &a : words) {
81 for (int i = 0; i <= a.size(); ++i) {
82 a.insert(a.begin() + i, first);
83 res.push_back(a);
84 a.erase(a.begin() + i);
85 }
86 }
87 return res;
88 }
89 };
90
91 void T046() {
92 vector<int>n;
93 Solution s;
94 n = { 1,2,3 };
95 for (auto &a : s.permute(n)) {
96 for (auto b : a)
97 cout << b << " ";
98 cout << endl;
99 }
100
101 }
