все возможные вариации из слова

#include<stdio.h>
#include<string.h>
#include<stdbool.h>

int next_permutation(char *p) {
  int a,b;
  for (a = strlen(p) - 2; a >= 0; --a)
    if (p[a] < p[a + 1])
      for (b = strlen(p) - 1;; --b)
        if (p[b] > p[a]) {
          int t = p[a];
          p[a] = p[b];
          p[b] = t;
          for (++a, b = strlen(p) - 1; a < b; ++a, --b) {
            t = p[a];
            p[a] = p[b];
            p[b] = t;
          }
          return true;
        }
  return false;
}



int main() {
    char p[] = {'M','U','P','\0'};

    while (next_permutation(p))
        printf("%s\n",p);

    return 0;
}

#include <algorithm>
#include <iostream>
#include <ostream>
#include <string>
using namespace std;

void print_all_permutations(const string& s)
{
    string s1 = s;
    sort(s1.begin(), s1.end()); 
    do {
        cout << s1 << endl;
    } while (next_permutation(s1.begin(), s1.end()));
}

int main()
{
    print_all_permutations("MUP");
}

MPU
MUP
PMU
PUM
UMP
UPM

import Data.List

f [] = [[]]
f xs = [x : ps | x <- xs, ps <- f (xs\\[x])]

import Data.List
f = permutations