全排列问题、八皇后问题、组合问题的递归解法

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全排列问题

#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;}

八皇后问题

#include <iostream>using namespace std;//#define LENGTH 8#define LENGTH 4void 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;}

组合问题

#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;}

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