Euler 37

gistfile1.txt

#!/usr/local/bin/node

// first, prep prime seive up to 1MM

n=1000000;
myPrimes = new Array();
for (i=2;i<=n;i++)
	{
	myPrimes[i]=true;
	}
for (i=2;i<=n;i++)
	{
	if (myPrimes[i])
		{
		for (j=2*i;j<=n;j+=i)
			{
			myPrimes[j]=false;
			}
		}	
	}
	
// then check if each prime is truncatable 
// if it is, add it to the appropriate de-duping array (circularsieve1 or 2)

circularsieve = [];
circularsieve2 = [];
for (i=11;i<=1000000;i+=2)
	{
	if (myPrimes[i])
		{
		truncater = i.toString();

// from left 

		for (j=1;j<=truncater.length-1;j++)
			{
			test = truncater.slice(j);
			if (truncater.indexOf("0")>=0)
				{
				break;
				}
			if(myPrimes[Number(test)]!=true)
				{
				break;
				}				
			if(myPrimes[Number(test)]==true && (j==truncater.length-1))
				{
				circularsieve[Number(truncater)] = true;
				}
			}		


// from right

		for (k=0;k<=truncater.length;k++)
			{
			test2 = truncater.slice(0,truncater.length-k);
			if (truncater.indexOf("0")>=0)
				{
				break;
				}
			if(myPrimes[Number(test2)]!=true)
				{
				break;
				}				
			if(myPrimes[Number(test2)]==true && (k==truncater.length-1))
				{
				circularsieve2[Number(truncater)] = true;
				}
			}		
		}
	}

sum = 0;
for (l=0;l<=1000000;l++)
	{
	if  (circularsieve[l] && circularsieve2[l])
		{
		console.log(l,"from both");
		sum += l;
		}
	}


console.log("total sum is", sum);