Palindrome Reorder.cpp

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;
using namespace std;

#define read freopen("input.txt", "r", stdin)
#define write freopen("output.txt", "w", stdout)

#define pb push_back
#define ll long long
#define ull unsigned long long
#define ld long double
#define pii pair<int, int>
#define vi vector<int>
#define vii vector<pii>
#define mpi map<int, int>
#define si set<int>
#define vt vector
#define getline cout << '\n'
#define all(x) x.begin(), x.end()

#define FOR(i, a, b) for (long long int i = a; (b - i) * (a - i) <= 0 && (b > a ? b != i : b != a); b > a ? i++ : i--)
#define FOREACH(it, m) for (auto it = m.rbegin(); it != m.rend(); it++)
#define FOREACHR(it, m) for (auto it = m.begin(); it != m.end(); it++)
// #define FOREACH(it, m) for (auto it : m)

// #define IOS ios_base::sync_with_stdio(false)

#define scanset(s, n) \
    FOR(i, 0, n)      \
    {                 \
        int x;        \
        cin >> x;     \
        s.insert(x);  \
    }

template <class T, size_t size>
// scan array
void scan(T (&array)[size])
{
    for (size_t i = 0; i < size; ++i)
        cin >> array[i];
}
template <class T, size_t size>
// print array
void print(const T (&array)[size])
{
    for (size_t i = 0; i < size; ++i)
        cout << array[i] << " ";
}
template <class T, size_t size>
void println(const T (&array)[size])
{
    print(array);
    cout << endl;
}
template <class T>
// scan vector with size
void scan(T &x)
{
    for (size_t i = 0; i < x.size(); i++)
    {
        cin >> x[i];
    }
}
template <class T>
// print vector
void print(const T &t)
{
    for (size_t i = 0; i < t.size(); i++)
        cout << t[i] << " ";
}
template <class T>
void println(const T &t)
{
    print(t);
    cout << endl;
}
template <class T>
// print vector, set, ...
void __print_collection(T const &container)
{
    for (auto pos : container)
        cout << pos << " ";
}

int main()
{
    string s;
    cin >> s;
    map<char, int> mp;
    for (auto i : s)
    {
        mp[i]++;
    }
    char x = '.';
    int c = 0;
    for (auto i : mp)
    {
        if (i.second % 2 == 1)
        {
            c++;
            x = i.first;
        }
    }
    if (c > 1)
    {
        cout << ("NO SOLUTION");
        return 0;
    }
    string ans;
    for (auto i : mp)
    {
        if (i.first == x)
            continue;
        FOR(j, 0, i.second / 2)
        ans += i.first;
    }
    if (x != '.')
        FOR(i, 0, mp[x])
    ans += x;
    FOREACH(i, mp)
    {
        if ((*i).first == x)
            continue;
        FOR(j, 0, (*i).second / 2)
        ans += (*i).first;
    }
    cout << (ans);
}