[笔试题]字符串的排列和组合

【代码】

 C++ Code 

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/*
    version: 1.0
    author: hellogiser
    blog: http://www.cnblogs.com/hellogiser
    date: 2014/9/22
*/

#include "stdafx.h"
#include "iostream"
#include <vector>
using namespace std;

void print(char *str)
{
    cout << str << endl;
}

void swap(char *a, char *b)
{
    char t = *a;
    *a = *b;
    *b = t;
}

//======================================================
// string permutation
// abc =======abc,acb,bac,bca,cab,cba
//======================================================
void permutation(char *str, int len, int index)
{
    if (index == len)
    {
        print(str);
    }
    else
    {
        for (int i = index; i < len; i++)
        {
            swap(str[index], str[i]);
            permutation(str, len, index + 1);
            swap(str[index], str[i]);
        }
    }
}

void Permutation(char *str)
{
    if(str == NULL || *str == '')
        return;
    int len = strlen(str);
    permutation(str, len, 0);
}

//======================================================
// string combination
// abc =========a,b,c,ab,ac,bc,abc
//======================================================
void print(vector<char> &result)
{
    vector<char>::iterator iter = result.begin();
    for (; iter != result.end(); iter++)
    {
        cout << *iter;
    }
    cout << endl;
}

void combination(char *str, int m, vector<char> &result)
{
    // exception  for example   C(1,2)
    if(str == NULL || *str == '' && m > 0)
        return;

    //base cases
    if (m == 0)
    {
        print(result);
        return;
    }
    //choose current char   C(n-1,m-1)
    result.push_back(*str);
    combination(str + 1, m - 1, result);

    // not choose current char  C(n-1,m)
    result.pop_back();
    combination(str + 1, m, result);
}

void Combination(char *str)
{
    if(str == NULL || *str == '')
        return;
    vector<char> result;
    int len = strlen(str);
    for (int i = 1; i <= len; i++)
    {
        combination(str, i, result);
    }
}

void test_permutation()
{
    char str[] = "abc";
    Permutation(str);
}

void test_combination()
{
    char str[] = "abc";
    Combination(str);
}

void test_main()
{
    test_permutation();
    cout << "========================== ";
    test_combination();
}

int main(void)
{
    test_main();
    return 0;
}
/*
abc
acb
bac
bca
cba
cab
==========================
a
b
c
ab
ac
bc
abc
*/

个人学习笔记，欢迎拍砖!---by hellogiser

Author: hellogiser

Blog: http://www.cnblogs.com/hellogiser/

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