Created
March 26, 2013 02:34
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Find the sum of all primes under 2,000,000 that contain a 7 or 9
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| var i, l, max = 2e6, primes = [], val = 0 | |
| function isPrime( n ) { | |
| var i = 2 | |
| if ( n < 2 ) return false | |
| if ( n == 2 ) return true | |
| for ( ; i < n; ++i ) | |
| if ( n % i === 0 ) | |
| return false | |
| return true | |
| } | |
| for ( i = 1; i < max; ++i ) | |
| if ( isPrime(i) ) | |
| primes.push(i) | |
| for ( i = 0, l = primes.length; i < l; ++i ) | |
| if ( /[7,9]/.test( '' + primes[i] ) ) | |
| val += primes[i] | |
| console.log(val) |
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| function sumPrimesWith7or9( n ) { | |
| var s = Math.sqrt(n), h = {}, val = 0, i = 3, j | |
| for ( ; i <= n; i += 2 ) { | |
| if ( h[( i - 3 ) / 2] ) continue | |
| if ( /[7,9]/.test( '' + i ) ) val += i | |
| if ( i > s ) continue | |
| for ( j = i * i; j <= n; j += i * 2 ) | |
| h[( j - 3 ) / 2] = 1 | |
| } | |
| return val | |
| } | |
| console.log(sumPrimesWith7or9(2e6)) |
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Kevins-MacBook-Pro-2:Euler kevin$ time node obvious.js
121784919393
real 9m32.194s
user 9m33.049s
sys 0m1.887s
Kevins-MacBook-Pro-2:Euler kevin$ time node optimized.js
121784919393
real 0m0.185s
user 0m0.163s
sys 0m0.022s