递归实现排列

留着明早省赛之前看

#include<iostream>
using namespace std;
int arr[10010];
int brr[10010];
int n,k;
void dfs(int num){
    if(num > n){
        for(int i = 1;i <= n;i++){
            cout << arr[i] << " ";
        }
        cout << endl;
        return;
    }
    for(int i = 1;i <= n;i++){
        if(brr[i] == 0){
            brr[i] = 1;
            arr[num] = i;
            dfs(num + 1);
            brr[i] = 0;
            arr[num]= 0;
        }
    }
}
int main()
{
    cin >> n >> k;
    dfs(1);
    return 0;
}

递归实现组合型枚举

#include<iostream>
using namespace std;
int arr[10010];
int brr[10010];
int n, k;
void dfs(int num,int start) {
    if(num - 1 + n - start + 1 < k){
        return;
    }
    if (num > k) {
        for (int i = 1; i <= k; i++) {
            cout << arr[i] << " ";
        }
        cout << endl;
        return;
    }
    for (int i = start; i <= n; i++) {
        arr[num] = i;
        dfs(num + 1, i + 1);
        arr[num] = 0;
    }
}
int main()
{
    cin >> n >> k;
    dfs(1,1);
    return 0;
}

递归实现指数

#include<iostream>
using namespace std;
int n;
int* arr = new int[10000] {0};
int main()
{
    void dfs(int);
    cin >> n;
    dfs(1);
}
void dfs(int x) {
    if (x > n) {
        for (int i = 1; i <= n; i++) {
            if (arr[i] == 1) {
                cout << i << " ";
            }
        }
        cout << endl;
        return;
    }
    arr[x] = 2;
    dfs(x + 1);
    arr[x] = 0;

    arr[x] = 1;
    dfs(x + 1);
    arr[x] = 0;
}