## Project Euler Problem #52

### April 30, 2010

Read the details of the problem here

**Summary**

Find the smallest positive integer, x, such that 2x, 3x, 4x, 5x, and 6x, contain the same digits in some order.

**Solution**

I used Groovy listops to drive this in, in essence, a single line within a loop. It was quick to write and “obviously correct” but very slow – taking 2.82 seconds. Using *as Set* is faster than using *groupBy()* to eliminate duplicates.

def ( i, answer ) = [ 1, 0 ] while (answer == 0) { answer = ( ((1..6).collect { (i * it).toString().toList().sort() } as Set) .size() == 1 ) ? i : 0 i++ }

Removing the reliance on the list operators, as per the solution below, brings the runtime down to 0.78 seconds. The code isn’t really any more complex.

def ( i, answer ) = [ 1, 0 ] while (answer == 0) { def s = (i.toString() as List).sort() for (j in 2..6) { if (s != (i * j).toString().toList().sort()) break if (j == 6) answer = i } i++ }

So that’s the two-for-one deal on this solution.

**Conclusion**

Groovy – You can take declarative logic, or some moderate performance. Take your pick.

**Note: **Putting this performance into context though, a port of the solutions to Ruby 1.8.7 has them running in 20.2 seconds and 4.55 seconds respectively. Running these scripts in JRuby 1.5.0 gives run times of 5.57 seconds and 1.60 seconds respectively. So both Groovy and the JVM scores very well in this regard.

May 26, 2010 at 14:20

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