SendMoreMoney.c

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

#define arr_size 8

void solve();
bool elementsUnique(int *arr, int size);
int compare(const void* a, const void* b);
bool isPairwiseDifferent(int *arr, int p, int size);

int main() {
  printf("(s,e,n,d,m,o,r,y)\n");
  solve();
  return 0;
}

  /*
   *	    S E N D
   * 	+   M O R E
   *      ------------
   * 	  M O N E Y
   * where M != 0 and every digit stands for a different (unique) number
   */

void solve() {
    for(int s = 0; s <= 9; s++) {
        for(int e = 0; e <= 9; e++) {
            for(int n = 0; n <= 9; n++) {
                for(int d = 0; d <= 9; d++) {
                    for(int m = 1; m <= 9; m++) { // [sic!]
                        for(int o = 0; o <= 9; o++) {
                            for(int r = 0; r <= 9; r++) {
                                for(int y = 0; y <= 9; y++) {
                                    // -----------------------------------------------------
                                    bool sumOK = s*1000  + e*100     + n*10  + d         +
                                                 m*1000  + o*100     + r*10  + e         ==
                                                 m*10000 + o*1000    + n*100 + e*10 + y;
                                    
                                    if(sumOK) {
                                        
                                        int result[arr_size] = {s,e,n,d,m,o,r,y};
                                        
                                        if(elementsUnique(result, arr_size)) {
                                            
                                            // Print result
                                            printf("%s", "(");
                                            for(int i = 0; i < arr_size-1; i++) {
                                                printf("%i,", result[i]);
                                            }
                                            printf("%i%s", result[arr_size-1], ")");
                                            return;
                                            
                                        }
                                        
                                    }
                                    // -----------------------------------------------------
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

bool elementsUnique(int *arr, int size) {
  // 1. copy
  int copy[size];
  for(int i = 0; i < size; i++) {
    copy[i] = arr[i];
  }
    
  // 2. sort
  qsort(copy, size, sizeof(int), compare);
    
  // 3. compare pairwise
  return isPairwiseDifferent(copy, 0, size);
}

int compare(const void* a, const void* b) {
  int int_a = *((int*) a);
  int int_b = *((int*) b);

  if (int_a == int_b) return 0;
  else if (int_a < int_b) return -1;
  else return 1;
}

bool isPairwiseDifferent(int *arr, int p, int size) {
  if(p == size - 1) {
    return true;
  }
  return arr[p] != arr[p+1] && isPairwiseDifferent(arr, p+1, size);
}