oral_quiz->#字符串的排列、组合#

///////////////////////////Permutation///////////////////////////////

#include <stdio.h>
#include <exception>

void Swap(char* p1, char* p2) {
	char temp = *p1;
	*p1 = *p2;
	*p2 = temp;
}

void Permutation_bad(char* pStr, char* pStart);
void Permutation(char* pStr) {
	if(pStr == NULL)
		return;

	Permutation_bad(pStr, pStr);
}

void Permutation_bad(char* pStr, char* pStart) {
	if(*pStart == '\0') {
		printf("%s.\n", pStr);
		return;
	}
	char* pIndex = pStart;
	while(*pIndex != '\0') {
		Swap(pStart, pIndex);
		Permutation_bad(pStr, pStart+1);
		Swap(pStart, pIndex);
		++pIndex;
	}
}

// ====================测试代码====================
void Test(char* pStr)
{
    if(pStr == NULL)
        printf("Test for NULL begins:\n");
    else
        printf("Test for %s begins:\n", pStr);

    Permutation(pStr);

    printf("\n");
}

int main(int argc, char* argv[])
{
    Test(NULL);

    char string1[] = "";
    Test(string1);

    char string2[] = "a";
    Test(string2);

    char string3[] = "ab";
    Test(string3);

    char string4[] = "abcd";
    Test(string4);

    return 0;
}

////////////////////////////Combination///////////////////////////

#include <stdio.h>
#include <exception>
#include <vector>
#include <string>

void Combination_m(char* pStr, int m, std::vector<char>& result);
void Combination(char* pStr) {
	if(pStr == NULL || pStr == '\0')
		return;
	int number = strlen(pStr);
	for(int i=1; i<=number; ++i) {
		std::vector<char> result;
		Combination_m(pStr, i, result);
	}
}

void Combination_m(char* pStr, int m, std::vector<char>& result) {
	if(pStr == NULL || (*pStr == '\0' && m != 0))
		return;
	if(m == 0) {
		for(std::vector<char>::iterator iter = result.begin(); iter<result.end(); ++iter)
			printf("%c", *iter);
		printf("\n");
		return;
	}
	//choose it
	result.push_back(*pStr);
	Combination_m(pStr+1, m-1, result);
	result.pop_back();
	//ignore it
	Combination_m(pStr+1, m, result);
}

// ====================测试代码====================
void Test(char* pStr)
{
    if(pStr == NULL)
        printf("Test for NULL begins:\n");
    else
        printf("Test for %s begins:\n", pStr);

    Combination(pStr);

    printf("\n");
}

int main(int argc, char* argv[])
{
    Test(NULL);

    char string1[] = "";
    Test(string1);

    char string2[] = "a";
    Test(string2);

    char string3[] = "ab";
    Test(string3);

    char string4[] = "abcd";
    Test(string4);

    return 0;
}