# Project Euler 038
# Largest 1–9 pandigital 9-digit number formed as concatenated product
# of an integer with (1,2,...,n) where n > 1.
function is_pandigital9(n: i64) -> bool {
if n < 100000000 || n > 999999999 { return false }
let mut seen: i32 = 0
let mut x: i64 = n
while x > 0 {
let d: i32 = (x % 10) as i32
if d == 0 { return false }
let bit: i32 = 1 << d
if (seen & bit) != 0 { return false }
seen = seen | bit
x = x / 10
}
return seen == 1022 # bits 1..9 set
}
function concat_prod(k: i64, n: i64) -> i64 {
let mut result: i64 = 0
let mut i: i64 = 1
while i <= n {
let mut part: i64 = k * i
# shift result left by digits of part
let mut p: i64 = part
let mut mul: i64 = 1
while p > 0 {
mul = mul * 10
p = p / 10
}
result = result * mul + part
if result > 999999999 { return -1 }
i = i + 1
}
return result
}
function main() -> i32 {
let mut best: i64 = 0
# n=2: k up to 4 digits; largest candidates near 9xxx
let mut k: i64 = 1
while k < 10000 {
let mut n: i64 = 2
while n <= 9 {
let v: i64 = concat_prod(k, n)
if v < 0 { break }
if is_pandigital9(v) && v > best {
best = v
}
n = n + 1
}
k = k + 1
}
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; }
bool is_pandigital9_i64(int64_t n);
int64_t concat_prod_i64_i64(int64_t k, int64_t n);
int32_t main(void);
bool is_pandigital9_i64(int64_t n) {
if ((n < 100000000 || n > 999999999)) {
return 0;
}
int32_t seen = 0;
int64_t x = n;
while (x > 0) {
int32_t d = ((int32_t)(FLOW_CHECKED_MOD((x), (10))));
if (d == 0) {
return 0;
}
int32_t bit = FLOW_CHECKED_SHL((1), (d));
if ((seen & bit) != 0) {
return 0;
}
seen = (seen | bit);
x = FLOW_CHECKED_DIV((x), (10));
}
return seen == 1022;
}
int64_t concat_prod_i64_i64(int64_t k, int64_t n) {
int64_t result = 0;
int64_t i = 1;
while (i <= n) {
int64_t part = (k * i);
int64_t p = part;
int64_t mul = 1;
while (p > 0) {
mul = (mul * 10);
p = FLOW_CHECKED_DIV((p), (10));
}
result = ((result * mul) + part);
if (result > 999999999) {
return (-1);
}
i = (i + 1);
}
return result;
}
int32_t main(void) {
int64_t best = 0;
int64_t k = 1;
while (k < 10000) {
int64_t n = 2;
while (n <= 9) {
int64_t v = concat_prod_i64_i64(k, n);
if (v < 0) {
break;
}
if ((is_pandigital9_i64(v) && v > best)) {
best = v;
}
n = (n + 1);
}
k = (k + 1);
}
printf("%lld\n", best);
return 0;
}