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| #include <stdio.h> | |
| #include <stdint.h> | |
| static int palindromic(uint64_t x) | |
| { | |
| uint64_t rev = 0; | |
| for (uint64_t tmp = x; tmp; tmp /= 10) { | |
| rev *= 10; | |
| rev += tmp % 10; | |
| } | |
| return x == rev; | |
| } | |
| int main() | |
| { | |
| uint64_t max = 0; | |
| uint64_t f_a, f_b, f_c, f_d; | |
| for (uint64_t r = 10000; r > 0; --r) | |
| for (uint64_t a = 99; a > 10; --a) | |
| for (uint64_t b = a; b > 10; --b) | |
| for (uint64_t c = b; c > 10; --c) | |
| for (uint64_t d = c; d > 10; --d) { | |
| uint64_t curr = a*b*c*d; | |
| if (curr < max) break; | |
| if (!palindromic(curr)) continue; | |
| max = curr; | |
| f_a = a; | |
| f_b = b; | |
| f_c = c; | |
| f_d = d; | |
| } | |
| printf("%lu * %lu * %lu * %lu = %lu\n", f_a, f_b, f_c, f_d, max); | |
| return 0; | |
| } |
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