求全排列和组合

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第一种方法耗费空间比较大，第二种方法更有技巧

方法一：

#include <iostream>
using namespace std;
#include <cstdio>
#include <cstdlib>

char a[100];
bool vis[100];
int ct[100];
int n;
int cst ;

void dfs(char a[],int i){
     if(i == n){
         for(int k = 0;k < n;k++)
         cout << a[ct[k]] << " ";
         cout << endl;
         cst ++;
         return ;
     }
     for(int j = 0;j < n;j++){
         if(!vis[j]){
             vis[j] = 1;
             ct[j] = i;
             dfs(a,i+1);
             vis[j] = 0;
             ct[j] = 0;
         }
     }
}

int main(){
    while(cin >> n){
         for(int i = 0;i < n;i++)
         cin >> a[i];
         memset(vis, 0, sizeof(vis));
         cst = 0;
         dfs(a,0);
         cout << cst << endl;
    }
    system("pause");
}

方法二：

#include <iostream>
using namespace std;
#include <cstdio>
#include <cstdlib>
#include <algorithm>

char a[100];
int   n,cst;
void swap(int &a, int &b){
     a = a^b;
     b = a^b;
     a = a^b;
}
void dfs(char a[],int k,int n){
      if(k == n){
         for(int p = 0;p < n;p++)
         cout << a[p] << " ";
         cout << endl;
         cst ++;
         return ;
      }
      for(int i = k;i < n;i++){
             swap(a[i],a[k]);
             dfs(a,k+1,n);
             swap(a[i],a[k]);
      }
}

int main(){
    while(cin >> n){
         cst = 0;
         for(int i = 0;i < n;i++)
         cin >> a[i];
         dfs(a,0,n);
         cout << cst << endl;
    }
    system("pause");
}

update:11-2

支持不输出重复的组合，如【1,1,1】只输出一次，上面那个会输出多次[方法错误]

#include <iostream>
using namespace std;
#include <cstdio>
#include <cstdlib>
#include <vector>
#include <algorithm>

void perm(vector<int> ct,int n, int k, vector<vector<int> > &cnt){
     if(k >= ct.size()){
            cnt.push_back(ct);
            return ;
     }
     for(int i = k;i < ct.size();i++){
             if(ct[i] == ct[k] && i != k)
             continue;
             swap(ct[i],ct[k]);
             perm(ct,n,k+1,cnt);
             swap(ct[i],ct[k]);
     }
}

int main(){
    int n,tmp;
    vector<int> ct;
    vector<vector<int> > cnt;
    while(cin >> n){
         ct.clear();
         cnt.clear();
         while(n--){
             cin >> tmp;
             ct.push_back(tmp);
         }
         perm(ct, n, 0, cnt);

         for(int i = 0;i < ct.size();i++)
         cout << ct[i] << " *" ;
         cout << endl;

         for(int i = 0;i < cnt.size();i++){
                for(int j = 0;j < cnt[i].size();j++){
                     cout << cnt[i][j] << " " ;
                }
                cout << endl;
         }
    }
}

下面才是正确的代码：

参加链接：http://www.zhizhihu.com/html/y2011/3674.html

#include <iostream>using namespace std;#include <cstdio>#include <cstdlib>/* 求排列 */int cnt;bool isok(int s[],int k,int i){     for(int j = k;j < i;j++)     if(s[j] == s[i])     return 1;     return 0;}void dfs(int s[], int k, int n){     if(k == n){        for(int i = 0;i < n;i++)        printf("%d ",s[i]);        printf("\n");        cnt++;        return;     }          for(int i = k;i < n;i++){         if(isok(s,k,i))         continue;         swap(s[i],s[k]);         dfs(s,k+1,n);         swap(s[i],s[k]);     }}int main(){    int s[100], n;    while(scanf("%d",&n) != EOF){         for(int i = 0;i < n;i++){               scanf("%d",&s[i]);                 }         cnt = 0;         dfs(s,0,n);         printf("cnt = %d\n",cnt);     }}

组合的过程:

#include <iostream>using namespace std;#include <cstdio>#include <cstdlib>#include <vector>int size;void dfs(vector<int> s,vector<int>& st,int pos,int n){     if(pos >= n){           for(int i = 0;i < st.size();i++)           printf("%d ",st[i]);           printf("\n");           size++;                  return;     }     dfs(s,st,pos+1,n);     st.push_back(s[pos]);     dfs(s,st,pos+1,n);     st.pop_back();}int  main(){     int n,key;     vector<int> s;     vector<int> st;     while(scanf("%d",&n) != EOF){         for(int i = 0;i < n;i++){            scanf("%d",&key);            s.push_back(key);         }         st.clear();         size = 0;         dfs(s,st,0,n);         printf("size = %d\n",size);     }     system("pause");}