递归

1.全排列递归

 1 #include<iostream>
 2 using namespace std;
 3 int n, arr[10], ifuse[10] = { 0,0,0,0,0,0,0,0,0,0 };
 4 void p()
 5 {
 6     for (int k = 1; k <= n; k++)
 7     {
 8         cout << arr[k] << " ";
 9     }cout << endl;
10 }
11 void f(int set)
12 {
13     if (set > n)return;
14     for (int i = 1; i <= n; i++)//每个位置上遍历1~n 
15     {
16         if (ifuse[i] == 0)
17         {
18             arr[set] = i;
19             ifuse[i] = 1;
20             f(set +1);
21         }
22         else continue;
23         if (set == n)p();
24         ifuse[i] = 0;
25     }
26 }
27 int main()
28 {
29     cin >> n;
30     f(1);
31 }

2.组合型递归

从1~m个数里选出n个数进行排列；

 1 #include<iostream>
 2 using namespace std;
 3 int m, n, arr[10];
 4 //一行一行的输出
 5 void p()
 6 {
 7     for (int k = 0; k < n; k++)
 8     {
 9         cout << arr[k] << " ";
10     }cout << endl;
11 }
12 //第i个位置最小值是j 
13 void f(int i, int j)
14 {
15     if (i >= n)return;
16     for (int a = j; a <= m - n + i + 1; a++)
17     {
18         arr[i] = a;
19         //        cout<<arr[i]<<" ";
20         f(i + 1, a + 1);
21         if (i == n - 1) p();
22     }
23 }
24 int main()
25 {
26     cin >> m >> n;
27     f(0, 1);
28 }

3.指数型递归

 1 //指数型递归
 2 #include<iostream>
 3 using namespace std;
 4 int n, arr[10];
 5 void p(int i)
 6 {
 7     for (int k = 0; k <= i; k++)
 8     {
 9         cout << arr[k] << " ";
10     }cout << endl;
11 }
12 //第i个位置的最小值是j
13 void f(int i, int j, int n)
14 {
15     if (j > n)return;
16     for (int a = j; a <= n; a++)
17     {
18         arr[i] = a;
19         p(i);
20         f(i + 1, a + 1, n);
21     }
22 }
23 int main()
24 {
25     cin >> n;
26     f(0, 1, n);
27 }