排列問題

//參考博客:
http://blog.csdn.net/yoer77/article/details/53458612
http://blog.csdn.net/cpfeed/article/details/7376132
http://blog.csdn.net/morewindows/article/details/7370155/

/* 遞歸+回溯(未去重) */
#include <iostream>
#include <cstring>
using namespace std;

void Perm(char s[],int k,int n)
{
    if(k == n-1)
    {
        for(int i = 0; i < n ;i++)
            cout<<s[i];
        cout<<endl;;
    }
    else
    {
        for(int i = k ; i < n; i++)
        {
            swap(s[k],s[i]);
            Perm(s,k+1,n);
            swap(s[k],s[i]);
        }
    }
}

int main()
{
    char s[] = "123";
    int len = strlen(s);
    Perm(s,0,len);
    return 0;
}

/* 遞歸+回溯(去重) */
#include <iostream>
#include <cstring>
using namespace std;

int count = 0;

bool IsSwap(char s[],int l,int r)
{
    for(int i = l ; i < r; i++)
    {
        if(s[i] == s[r])
            return false;
    }
    return true;
}

void Perm(char s[],int k,int n)
{
    if(k == n-1)
    {
        for(int i = 0; i < n; i++)
            cout<<s[i];
        count++;
        cout<<endl;
    }
    else
    {
        for(int i = k; i < n; i++)
        {
            if(IsSwap(s,k,i))
            {
                swap(s[k],s[i]);
                Perm(s,k+1,n);
                swap(s[k],s[i]);
            }
        }
    }
}

int main()
{
    char s[] = "1232";
    int len = strlen(s);
    Perm(s,0,len);
    cout<<count<<endl;
    return 0;
}
/* dfs深搜(未去重) */
#include <iostream>
#include <cstring>
using namespace std;

#define maxn 100
char perm[maxn];
int visit[maxn];
char s[] = "abcd";
int count = 0;

void dfs(int step,int n)
{
    if(step == n)
    {
        for(int i = 0; i < n; i++)
            cout<<s[perm[i]];
        count++;
        cout<<endl;
    }
    else
    {
        for(int i = 0; i < n; i++)
        {
            if(!visit[i])
            {
                perm[step] = i;
                visit[i] = 1;
                dfs(step+1,n);
                visit[i] = 0;
            }
        }
    }
}

int main()
{
    int n = strlen(s);
    memset(perm,0,sizeof(perm));
    memset(perm,0,sizeof(visit));
    dfs(0,n);
    cout<<count<<endl;
    return 0;
}
/* 字典序 */
#include <iostream>
#include <cstring>
using namespace std;

void Reverse(char *i,char *j)
{
    while(i < j)
    {
        swap(*i,*j);
        i++; j--;
    }
}

bool Next_permutation(char s[])
{
    int len = strlen(s);
    if(!len) return false;
    char *pEnd,*p,*q,*pFind;
    pEnd = s + len-1;
    p = pEnd;
    while(p != s)
    {
        q = p;
        p--;
        while(*p < *q)
        {
            pFind = pEnd;
            if(*pFind < *p)
                pFind--;
            swap(*p,*pFind);
            Reverse(q,pEnd);
            return true;
        }
    }
    Reverse(s,pEnd);
    return false;
}

int main()
{
    char s[] = "123";
    do
    {
        cout<<s<<endl;
    }while(Next_permutation(s));
    return 0;
}