next_permutation,memcmp,memcpy

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#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>using namespace std;int main(){      int ncase, n, m, a[] = {1, 2, 3, 4, 5, 6, 7, 8, 9}, buf[10];      cin >> ncase;      while (ncase--)      {            cin >> n >> m;            memcpy(buf, a, sizeof(int)*n);            //将数组a的前n个元素拷贝到buf的前n个元素中            for (int i=0; i<m; i++)                  printf("%d", a[i]);            printf("\n");            while (next_permutation(a, a+n))//数组a前n个元素的下一个排列            {                  if (memcmp(a, buf, sizeof(int)*m)!=0)                  //比较数组a的前n个元素与buf的前m个元素是否相等                  {                        for (int i=0; i<m; i++)                              printf("%d", a[i]);                        printf("\n");                        memcpy(buf, a, sizeof(int)*n);                  }            }      }      return 0;}