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Find the greatest product of five consecutive digits in the 1000-digit number

April 19, 2008

Find the greatest product of five consecutive digits in the 1000-digit number.

73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450

Solution 1

<?php

$num = "731671765313306249192251196744265747423553491949349698352031277450632 6239578318016984801869478851843858615607891129494954595017379583319528 5320880551112540698747158523863050715693290963295227443043557668966489 5044524452316173185640309871112172238311362229893423380308135336276614 2828064444866452387493035890729629049156044077239071381051585930796086 6701724271218839987979087922749219016997208880937766572733300105336788 1220235421809751254540594752243525849077116705560136048395864467063244 1572215539753697817977846174064955149290862569321978468622482839722413 7565705605749026140797296865241453510047482166370484403199890008895243 4506585412275886668811642717147992444292823086346567481391912316282458 6178664583591245665294765456828489128831426076900422421902267105562632 1111109370544217506941658960408071984038509624554443629812309878799272 4428490918884580156166097919133875499200524063689912560717606058861164 6710940507754100225698315520005593572972571636269561882670428252483600 823257530420752963450";

$l = array();

for($i = 0; $i < 995; $i++)
{
        $part = substr($num, $i, 5);
        $part = preg_split(‘//’, $part, -1, PREG_SPLIT_NO_EMPTY);
        $l[] = array_product($part);
}

sort($l, SORT_NUMERIC);
reset($l);
echo end($l);

?>

Written by Danltn · Filed Under PHP, ProjectEuler 

Add all the natural numbers below one thousand that are multiples of 3 or 5

April 19, 2008

Quote from Project Euler website:

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

Here are some of my PHP based solutions:

Solution 1a (minimised)

for($i=1,$a=0;$i<1000;$i++){if(!($i%3)or!($i%5))$a+=$i;}echo$a;

Solution 1b (beautified)

<?php

for ($i = 1, $a = 0; $i < 1000; $i++)
{
if (!($i % 3) or !($i % 5))
$a += $i;
}
echo $a;

?>

Solution 2 (minimised)(faster)

echo array_sum(array_unique(array_merge(range(3,999,3),range(5,999,5))));
 

Written by Danltn · Filed Under PHP, ProjectEuler 

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