47 lines
1.3 KiB
C
47 lines
1.3 KiB
C
/* A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.
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*
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* Find the largest palindrome made from the product of two 3-digit numbers.*/
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#define _POSIX_C_SOURCE 199309L
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#include <stdio.h>
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#include <stdlib.h>
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#include <time.h>
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#include "projecteuler.h"
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int main(int argc, char **argv)
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{
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int i, j, max = 0, num;
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double elapsed;
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struct timespec start, end;
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clock_gettime(CLOCK_MONOTONIC, &start);
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/* Using a brute-force approach: generate every product of 3-digit numbers
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* and check if it's palindrome. If the product found is greater than the
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* current maximum, save the current product.*/
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for(i = 999; i >= 100; i--)
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{
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for(j = i; j >= 100; j--)
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{
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num = i * j;
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/* Use the function defined in projecteuler.c to check if a number is palindrome.*/
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if(num > max && is_palindrome(num, 10))
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{
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max = num;
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}
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}
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}
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clock_gettime(CLOCK_MONOTONIC, &end);
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elapsed = (end.tv_sec - start.tv_sec) + (double)(end.tv_nsec - start.tv_nsec) / 1000000000;
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printf("Project Euler, Problem 4\n");
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printf("Answer: %d\n", max);
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printf("Elapsed time: %.9lf seconds\n", elapsed);
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return 0;
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}
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