題目：https://www.luogu.org/problemnew/show/P1215

令三元組(i,j,k)表示該情況是否出現，即可防止死迴圈

注意0這個答案有可能是合法的，答案要加上

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;
inline int read()
{
  int ans = 0,op = 1;
  char ch = getchar();
  while(ch < '0' || ch > '
 
9')
    {
      if(ch == '-') op = -1;
      ch = getchar();
    }
  while(ch >= '0' && ch <= '9')
    {
      (ans *= 10) += ch - '0';
      ch = getchar();
    }
  return ans * op;
}
bool ok[21][21][21];
bool e[21];
int a,b,c;
void dfs(int i,int j,int k)
{
  if(i < 0 || j < 0 || k < 0
 
 || i > a || j > b || k > c) return;
  if(ok[i][j][k]) return;
  if(i == 0) e[k] = 1;
  ok[i][j][k] = 1;
  
  dfs(i - (b - j),b,k);
  dfs(0,i + j,k);
  dfs(i,j - (c - k),c);
  dfs(i,0,j + k);
  dfs(a,j,k - (a - i));
  dfs(i + k,j,0);
  
  dfs(a,j - a + i,k);
  dfs(i + j,0,k);
  dfs(i,b,k - b + j);
  dfs(i,j 
 
+ k,0);
  dfs(i - c + k,j,c);//1 -> 3
  dfs(0,j,i + k);
}
int main()
{
  a = read(),b = read(),c = read();
  dfs(0,0,c);
  for(int i = 0;i <= c;i++) if(e[i]) printf("%d ",i);
  return 0;
 }