回文数字(递归求解，又臭又长，慎点)

#include<iostream>

#include<string>

using namespace std;

int n;

string sub(string s)

{

string m;

for (int i = s.length()-1; i >= 0; i--)

{

m += s[i];

}

return m;

}

void fund(int num,int m,string s,bool b)

{

if (num <= 2)

{

if (m < 0)

return;

if (num == 1)

{

if (m < 10 )

{

char a = m + '0';

string l = sub(s);

s += a;

s += l;

cout << s << endl;

}

}

else

{

if (m <= 18 && m % 2 == 0)

{

char a = m/2 + '0';

string l = sub(s);

s += a;

s += a;

s += l;

cout << s << endl;

}

}

return;

}

int i;

if(b == false)

{

i = 1;

}

else

i = 0;

for (; i < 10; i++)

{

m -= 2 * i;

char a = i + '0';

s += a;

fund(num - 2, m, s,true);

s = s.substr(0, s.size() - 1);

m += 2 * i;

}

}

int main()

{

cin >> n;

if (n < 5 || n>54)

{

cout << -1;

return 0;

}

string s = "";

fund(5, n, s,false);

fund(6, n, s,false);

return 0;

}