全排列问题、八皇后问题、组合问题的递归解法

#include <iostream>

using namespace std;

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

void find_core(char* col, char* begin){
if (*begin == '\0'){
cout << col << endl;
}
else{
for (char *ch = begin; *ch != '\0'; ++ch){
swap(ch, begin);
find_core(col, begin + 1);
swap(ch, begin);
}
}
}

void find(char *col){
find_core(col, col);
}

int main(){
//char col[10] = "01234567";
//char col[10] = "0123";
char col[] = "abc";

find(col);

int ttt = 0;
return 0;
}

#include <iostream>

using namespace std;

//#define LENGTH 8
#define LENGTH 4

void print(int *a){
for (int i = 0; i < LENGTH; ++i)
cout << a[i];
cout << endl;
}

void swap(int &a, int &b){
int tmp = a;
a = b;
b = tmp;
}

bool check_valid(int *col){
bool flag = true;
for (int i = 0; i < LENGTH - 1; ++i){
for (int j = i + 1; j < LENGTH; ++j){
if (col[i] - col[j] == i - j || col[i] - col[j] == j - i){
flag = false;
break;
}
}
if (!flag)
break;
}
return flag;
}

void find_core(int *col, int k){
if (k == LENGTH){ //if (k == LENGTH - 1)也可以
if (check_valid(col))
print(col);
}
else{
for (int i = k; i < LENGTH; ++i){
swap(col[i], col[k]);
find_core(col, k + 1);
swap(col[i], col[k]);
}
}
}

void find(int *col){
find_core(col, 0);
}

int main(){
//int col[] = {0, 1, 2, 3, 4, 5, 6, 7};
int col[] = {0, 1, 2, 3};

find(col);

int ttt = 0;
return 0;
}

#include <iostream>

using namespace std;

void find_core(char *a, int m, int start, char *buf){
if (m > strlen(a) - start)
return;

if (m == 0)
{
cout << buf << endl;
}
else
{
//start位置的字符为组合中的字符
int last_len = strlen(buf);
buf[last_len] = a[start];
buf[last_len + 1] = '\0';
find_core(a, m - 1, start + 1, buf);

//start位置的字符不为组合中的字符
buf[last_len] = '\0';
find_core(a, m, start + 1, buf);
}
}

void find(char *a, int m){
char *buf = new char [m + 1];
memset(buf, '\0', m + 1);
find_core(a, m, 0, buf);
}

int main(){
char a[] = "abc";

find(a, 2);

int ttt = 0;

return 0;
}