Acwing 93. 递归实现组合型枚举

 u + n - start < m 为剪枝操作，当前已选择的数 + 剩下的数 凑不出指定的个数m，直接return

#include <cstdio>

const int N = 30;

int path[N];
int n, m;

void dfs(int u, int start)
{
    if (u + n - start < m) return ;
    
    if (u == m + 1)
    {
        for (int i = 1; i <= m; ++ i) printf("%d ", path[i]);
        printf("\n");
        return ;
    }
    
    for (int i = start; i <= n; ++ i)
    {
        path[u] = i;
        dfs(u + 1, i + 1);
        path[u] = 0;
    }
}

int main()
{
    scanf("%d %d", &n, &m);
    
    dfs(1, 1);
    
    return 0;
}