C#算法之全排列递归算法实例讲解

{ 1 2 3}
{ 1 3 2 }
{ 2 1 3 }
{ 2 3 1 }
{ 3 2 1 }
{ 3 1 2 }

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#include <iostream>
using namespace std;

int sum = 0;//记录有多少种组合

void Swap(char str[], int a, int b)
{
    char temp = str[a];
    str[a] = str[b];
    str[b] = temp;
}

void Perm(char str[], int begin, int end)
{
    if (begin == end)
    {
        for (int i = 0; i <= end; i++)
        {
            cout << str[i];
        }
        cout << endl;
        sum++;
        return;
    }
    else
    {
        for (int j = begin; j <= end; j++)
        {
            Swap(str, begin, j);
            Perm(str, begin + 1, end);
            Swap(str, j, begin);
        }
    }
}

int main()
{
    int n;
    char c[16];
    char tmp;

    cin >> n;
    tmp = getchar();    // 接受回车
    if (1 <= n && n <= 15) {
        for (int i = 0; i < n; i++) {
            c[i] = getchar();
        }
        Perm(c, 0, n - 1);
    }
    cout << sum;
    cout << endl;
    return 0;
}

#include <iostream>
using namespace std;

int sum=0;//记录有多少种组合

void Swap(char str[], int a, int b)
{
    char temp = str[a];
    str[a] = str[b];
    str[b] = temp;
}

bool IsSwap(char *pchar, int nBegin, int nEnd)
{
    for (int i = nBegin; i < nEnd; i++)
        if (pchar[i] == pchar[nEnd])
            return false;
    return true;
}

void Perm(char str[], int begin, int end)
{
    if (begin==end)
    {
        for (int i = 0; i <= end; i++)
        {
            cout << str[i];
        }
        cout << endl;
        sum++;
        return;
    }
    else
    {
        for (int j = begin; j <= end; j++)
        {
            if (IsSwap(str, begin, j))
            {
                Swap(str, begin, j);
                Perm(str, begin + 1, end);
                Swap(str, j, begin);
            }
        }
    }
}

int main()
{
    int n;
    char c[16];
    char tmp;

    cin >> n;
    tmp = getchar();    // 接受回车
    if (1 <= n && n <= 15) {
        for (int i = 0; i < n; i++) {
            c[i] = getchar();
        }
        Perm(c, 0, n - 1);
    }
    cout << sum;
    cout << endl;
    return 0;
}

//全排列的非递归实现
#include <iostream>
using namespace std;
void Swap(char *a, char *b)
{
    char t = *a;
    *a = *b;
    *b = t;
}
//反转区间
void Reverse(char *a, char *b)
{
    while (a < b)
        Swap(a++, b--);
}
//下一个排列
bool Next_permutation(char a[])
{
    char *pEnd = a + strlen(a);
    if (a == pEnd)
        return false;
    char *p, *q, *pFind;
    pEnd--;
    p = pEnd;
    while (p != a)
    {
        q = p;
        --p;
        if (*p < *q) //找降序的相邻2数,前一个数即替换数
        {
            //从后向前找比替换点大的第一个数
            pFind = pEnd;
            while (*pFind <= *p)
                --pFind;
            //替换
            Swap(pFind, p);
            //替换点后的数全部反转
            Reverse(q, pEnd);
            return true;
        }
    }
    Reverse(p, pEnd);//如果没有下一个排列,全部反转后返回true
    return false;
}
int QsortCmp(const void *pa, const void *pb)
{
    return *(char*)pa - *(char*)pb;
}
int main()
{
    int sum = 0;
    char szTextStr[16];
    cin >> szTextStr;
    char tmp = getchar();    // 接受回车
   
    //加上排序
    qsort(szTextStr, strlen(szTextStr), sizeof(szTextStr[0]), QsortCmp);
    int i = 1;
    cout << endl << endl << endl;
    do{
        cout<<szTextStr<<endl;
        sum++;
    } while (Next_permutation(szTextStr));

    cout << sum<<endl;
    return 0;
}