# Project Euler 041
# Largest n-digit pandigital prime.
import euler.nt { is_prime }
function swap(a: ptr<i32>, i: i32, j: i32) -> void {
let t: i32 = a[i]
a[i] = a[j]
a[j] = t
}
function next_perm(a: ptr<i32>, n: i32) -> bool {
# lexicographic next permutation; returns false if finished
let mut i: i32 = n - 2
while i >= 0 && a[i] >= a[i + 1] {
i = i - 1
}
if i < 0 { return false }
let mut j: i32 = n - 1
while a[j] <= a[i] {
j = j - 1
}
swap(a, i, j)
let mut l: i32 = i + 1
let mut r: i32 = n - 1
while l < r {
swap(a, l, r)
l = l + 1
r = r - 1
}
return true
}
function to_number(a: ptr<i32>, n: i32) -> i64 {
let mut v: i64 = 0
for i in 0..n {
v = v * 10 + (a[i] as i64)
}
return v
}
function main() -> i32 {
# 8- and 9-digit pandigitals are divisible by 3 (digit sum), so max is 7-digit
let digits: array<i32, 7> = [7, 6, 5, 4, 3, 2, 1] # start from largest
let mut best: i64 = 0
# iterate permutations in descending order by starting high and using prev...
# easier: generate all from ascending then track max prime
let asc: array<i32, 7> = [1, 2, 3, 4, 5, 6, 7]
while true {
let v: i64 = to_number(asc, 7)
if is_prime(v) && v > best {
best = v
}
if !next_perm(asc, 7) {
break
}
}
printf("%lld\n", best)
return 0
}
Generated C
#include <stdint.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* Flow runtime helpers */
typedef struct flow_temp_node { struct flow_temp_node* next; } flow_temp_node;
static flow_temp_node* flow_temp_head = NULL;
static int flow_temp_atexit_set = 0;
__attribute__((unused)) static void flow_temp_free_all(void) {
while (flow_temp_head) {
flow_temp_node* n = flow_temp_head;
flow_temp_head = n->next;
free(n);
}
}
__attribute__((unused)) static void* flow_temp_alloc(size_t nbytes) {
flow_temp_node* node = (flow_temp_node*)malloc(sizeof(flow_temp_node) + nbytes);
if (!node) return NULL;
node->next = flow_temp_head;
flow_temp_head = node;
if (!flow_temp_atexit_set) {
flow_temp_atexit_set = 1;
atexit(flow_temp_free_all);
}
return (void*)(node + 1);
}
#ifndef FLOW_DIAG
#define FLOW_DIAG(msg) fprintf(stderr, "%s", (msg))
#endif
#ifndef FLOW_LOG
#define FLOW_LOG(fmt, ...) printf(fmt, __VA_ARGS__)
#endif
#ifndef FLOW_LOG_EMPTY
#define FLOW_LOG_EMPTY(fmt) printf(fmt)
#endif
static char* flow_strcat(const char* a, const char* b) {
size_t la = strlen(a ? a : ""), lb = strlen(b ? b : "");
char* r = (char*)flow_temp_alloc(la + lb + 1);
if (!r) return NULL;
if (la) memcpy(r, a, la);
if (lb) memcpy(r + la, b, lb);
r[la + lb] = '\0';
return r;
}
#define __flow_in_arr(arr, val) __extension__ ({ \
int _found = 0; \
size_t _n = sizeof(arr)/sizeof((arr)[0]); \
for (size_t _i = 0; _i < _n; _i++) { \
if ((arr)[_i] == (val)) { _found = 1; break; } \
} _found; })
/* Unified fault handler (MISRA #279) — override with -DFLOW_FAULT_HANDLER=fn */
#ifndef FLOW_FAULT_HANDLER
__attribute__((unused)) static inline void flow_fault_handler(const char* msg) {
fprintf(stderr, "flow: %s\n", msg ? msg : "fault");
abort();
#if defined(__GNUC__) || defined(__clang__)
__builtin_unreachable();
#endif
}
#else
#define flow_fault_handler FLOW_FAULT_HANDLER
#endif
#define flow_div_by_zero_handler() flow_fault_handler("division by zero")
#define flow_shift_ub_handler() flow_fault_handler("invalid shift (amount out of range or left-shift of negative)")
#ifndef FLOW_CHECKED_DIV
#define FLOW_CHECKED_DIV(L, R) (((R) != 0) ? ((L) / (R)) : (flow_div_by_zero_handler(), (L) * 0))
#endif
#ifndef FLOW_CHECKED_MOD
#define FLOW_CHECKED_MOD(L, R) (((R) != 0) ? ((L) % (R)) : (flow_div_by_zero_handler(), (L) * 0))
#endif
#ifndef FLOW_CHECKED_SHL
#define FLOW_CHECKED_SHL(L, R) ((((R) >= 0) && ((unsigned long long)(R) < (sizeof(L) * 8ull)) && ((L) >= 0)) ? ((L) << (R)) : (flow_shift_ub_handler(), (L) * 0))
#endif
#ifndef FLOW_CHECKED_SHR
#define FLOW_CHECKED_SHR(L, R) ((((R) >= 0) && ((unsigned long long)(R) < (sizeof(L) * 8ull))) ? ((L) >> (R)) : (flow_shift_ub_handler(), (L) * 0))
#endif
#include <math.h>
void* _ui_state = NULL;
static inline float i32_to_f32(int32_t v) { return (float)v; }
/* Host stub for @gpu kernels (device codegen replaces this). */
static inline int32_t gpu_thread_id(void) { return 0; }
int64_t gcd_i64_i64(int64_t a0, int64_t b0);
int64_t lcm_i64_i64(int64_t a, int64_t b);
int64_t isqrt_i64(int64_t n);
int64_t mulmod_i64_i64_i64(int64_t a0, int64_t b0, int64_t mod);
int64_t mod_pow_i64_i64_i64(int64_t base, int64_t exp, int64_t mod);
bool is_prime_i64(int64_t n);
void swap_ptr_i32_i32_i32(int32_t* a, int32_t i, int32_t j);
bool next_perm_ptr_i32_i32(int32_t* a, int32_t n);
int64_t to_number_ptr_i32_i32(int32_t* a, int32_t n);
int32_t main(void);
int64_t gcd_i64_i64(int64_t a0, int64_t b0) {
int64_t a = a0;
int64_t b = b0;
while (b != 0) {
int64_t t = FLOW_CHECKED_MOD((a), (b));
a = b;
b = t;
}
return a;
}
int64_t lcm_i64_i64(int64_t a, int64_t b) {
if ((a == 0 || b == 0)) {
return 0;
}
return (FLOW_CHECKED_DIV((a), (gcd_i64_i64(a, b))) * b);
}
int64_t isqrt_i64(int64_t n) {
if (n < 2) {
return n;
}
int64_t x = n;
int64_t y = FLOW_CHECKED_DIV(((x + 1)), (2));
while (y < x) {
x = y;
y = FLOW_CHECKED_DIV(((x + FLOW_CHECKED_DIV((n), (x)))), (2));
}
return x;
}
int64_t mulmod_i64_i64_i64(int64_t a0, int64_t b0, int64_t mod) {
int64_t a = FLOW_CHECKED_MOD((a0), (mod));
int64_t b = FLOW_CHECKED_MOD((b0), (mod));
int64_t result = 0;
while (b > 0) {
if (FLOW_CHECKED_MOD((b), (2)) == 1) {
result = FLOW_CHECKED_MOD(((result + a)), (mod));
}
a = FLOW_CHECKED_MOD(((a * 2)), (mod));
b = FLOW_CHECKED_DIV((b), (2));
}
return result;
}
int64_t mod_pow_i64_i64_i64(int64_t base, int64_t exp, int64_t mod) {
if (mod == 1) {
return 0;
}
int64_t result = 1;
int64_t b = FLOW_CHECKED_MOD((base), (mod));
int64_t e = exp;
while (e > 0) {
if (FLOW_CHECKED_MOD((e), (2)) == 1) {
result = mulmod_i64_i64_i64(result, b, mod);
}
b = mulmod_i64_i64_i64(b, b, mod);
e = FLOW_CHECKED_DIV((e), (2));
}
return result;
}
bool is_prime_i64(int64_t n) {
if (n < 2) {
return 0;
}
if (n < 4) {
return 1;
}
if ((FLOW_CHECKED_MOD((n), (2)) == 0 || FLOW_CHECKED_MOD((n), (3)) == 0)) {
return 0;
}
int64_t i = 5;
while ((i * i) <= n) {
if ((FLOW_CHECKED_MOD((n), (i)) == 0 || FLOW_CHECKED_MOD((n), ((i + 2))) == 0)) {
return 0;
}
i = (i + 6);
}
return 1;
}
void swap_ptr_i32_i32_i32(int32_t* a, int32_t i, int32_t j) {
int32_t t = a[i];
a[i] = a[j];
a[j] = t;
}
bool next_perm_ptr_i32_i32(int32_t* a, int32_t n) {
int32_t i = (n - 2);
while ((i >= 0 && a[i] >= a[(i + 1)])) {
i = (i - 1);
}
if (i < 0) {
return 0;
}
int32_t j = (n - 1);
while (a[j] <= a[i]) {
j = (j - 1);
}
swap_ptr_i32_i32_i32(a, i, j);
int32_t l = (i + 1);
int32_t r = (n - 1);
while (l < r) {
swap_ptr_i32_i32_i32(a, l, r);
l = (l + 1);
r = (r - 1);
}
return 1;
}
int64_t to_number_ptr_i32_i32(int32_t* a, int32_t n) {
int64_t v = 0;
int32_t __flow_step_1 = 1;
for (int32_t i = 0; (0 <= n) ? i < n : i > n; i += (0 <= n) ? 1 : -1) {
v = ((v * 10) + ((int64_t)(a[i])));
}
return v;
}
int32_t main(void) {
int32_t digits[7] = { 7, 6, 5, 4, 3, 2, 1 };
int64_t best = 0;
int32_t asc[7] = { 1, 2, 3, 4, 5, 6, 7 };
while (1) {
int64_t v = to_number_ptr_i32_i32(asc, 7);
if ((is_prime_i64(v) && v > best)) {
best = v;
}
if ((!(next_perm_ptr_i32_i32(asc, 7)))) {
break;
}
}
printf("%lld\n", best);
return 0;
}