dfs 的全排列

 #include <iostream>
 #include <algorithm>
 #include <cstdio>
 #include <string>
 #include <string>
 #include <cstring>
 #include <map>
 #include <utility>
 using namespace std;
 const int  N = 1e2+ ;
 bool vis[N];
 int a[N],n;
 void dfs(int num,int n){
     if(num==n){
         for(int  i =;i<n;i++){
             printf("%d%c",a[i],i==n-?'\n':' ');
         }
         return ;
     }
     for(int  i=;i<=n;i++){
         if(!vis[i]){
             vis[i]=;
             a[num]=i;
             dfs(num+,n);
             vis[i]=;
         }
     }
 }
 int  main()
 {
     while(~scanf("%d",&n)){
         memset(vis,,sizeof(vis));
         dfs(,n);
     }
     return  ;
  } 

 //用于生成全排列的函数
 int a[N],n;
 void init()
 {
     for(int   i=;i<;i++){
         a[i]=i+;
     }
 }
 int main()
 {
     init();
     int cnt=;
     do{
         for(int   i=;i<;i++)
         printf("%d%c",a[i],i==?'\n':' ');
         cnt++;
     }while(next_permutation(a,a+));
     printf("%d\n",cnt);
     return ;
 }

 //从1到n取出m个数
 #include <iostream>
 #include <algorithm>
 #include <cstdio>
 #include <string>
 #include <string>
 #include <cstring>
 #include <map>
 #include <utility>
 using namespace std;
 const int  N = 1e2+ ;
 bool vis[N];
 int n,m,a[N];
 void dfs(int  num,int n){
     if(num==m+){
         for(int  i =;i<=m;i++)
         {
             printf("%d%c",a[i],i==m?'\n':' ');
         }
         return ;
     }
     for(int i =a[num-]+;i<=n;i++){
         if(!vis[i]){
             vis[i]=;
             a[num]=i;
             dfs(num+,n);
             vis[i]=;
         }
     }
 }
 int  main()
 {
     while(~scanf("%d%d",&n,&m)){
         memset(vis,,sizeof(vis));
         dfs(,n);
     }
     return  ;
 }

 //有重复字符的全排列

 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
 #include <iostream>
 #include <algorithm>
 using namespace std;
 const int N=1e3+;
 char s[N],buf[N];
 int l;
 bool vis[N];
 void dfs(int num){
     if(num==l){
         printf("%s\n",buf);
         return  ;
     }
     for(int i =;i<l;i++){
         if(!vis[i]){
             int j;
             for(j=i+;j<l;j++){
                 if(vis[j]&&s[i]==s[j]){//重复：先用了s靠后的字符又满足字符一样
                     break;
                 }
             }
             if(j==l){
                 vis[i]=;
                 buf[num]=s[i];
                 dfs(num+);
                 vis[i]=;
             }
         }
     }

 }
 int  main()
 {
     while(~scanf("%s",s)){
         memset(vis,,sizeof(vis));
         l =strlen(s);
         buf[l]='\0';
         dfs();
     }
     return ;
 }

 //hdu   1016

 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
 #include <iostream>
 #include <algorithm>
 using namespace std;
 const int N=1e2+;
 int n;
 bool vis[N];
 int a[N];
 bool prime(int n){
     if(n==) return false;
     for(int i =;i*i<=n;i++){
         if(n%i==) return  false;
     }
     return true;
 }
 void  dfs(int num,int n){
     if(num==n&&prime(+a[n-])){
         for(int i =;i<n;i++){
             printf("%d%c",a[i],i==n-?'\n':' ');
         }
         return ;
     }
     for(int   i=;i<=n;i++){//1一定是第一个
         if(!vis[i]&&prime(i+a[num-])){
             vis[i]=;
             a[num]=i;
             dfs(num+,n);
             vis[i]=;
         }
     }
 }
 int f=;
 int main()
 {
     while(~scanf("%d",&n)){
         memset(vis,,sizeof(vis));
         a[]=;
         printf("Case %d:\n",f++);
         dfs(,n);
         printf("\n");
     }
     return ;
 }

 #include<cstdio>
 #include<algorithm>
 #include<cstring>
 #include<cmath>
 #include<iostream>
 #include<vector>
 #include <cstdlib>
 #include <map>
 using namespace std;
 #define mem(a,b) memset(a,b,sizeof(a))
 const int N = 2e5+;
 pair<int,int>P;
 vector<int> ve[N];
 vector<pair<int,int> > que[N];
 int  a[N],b[N];
 int m;
 int n,sum;
 bool vis[N];
 int cnt  = ;
 map<int,int>mp;
 //从数组b里面取出若干个数，令其和为110
 void dfs(int num,int n){
     {
         if(num<=n&&sum==)
         {

             for(int j=;j<=num-;j++){
                 printf("%d ",a[j]);
             }
             printf(":: %d \n",sum);

             return ;
         }
         for(int i =mp[a[num-]]+;i<=n;i++){
             if(!vis[i]){
                 vis[i] = ;
                 a[num]= b[i];
                 sum+=b[i];
                 dfs(num+,n);
                 vis[i] = ;
                 sum-=b[i];
             }
         }
     }
 }
 int main()
 {
  sum =;
  mp[]=;
 // scanf("%d%d",&n,&m);
 scanf("%d",&n);
 for(int i =;i<=n;i++){
     scanf("%d",&b[i]);
     mp[b[i]] =i;
 }
     dfs(,n);
     return ;
 }