Initial data commit

Task/Truncatable-primes/Java/truncatable-primes.java

@@ -0,0 +1,69 @@
+import java.util.BitSet;
+
+public class Main {
+
+	public static void main(String[] args){
+
+		final int MAX = 1000000;
+
+		//Sieve of Eratosthenes (using BitSet only for odd numbers)
+		BitSet primeList = new BitSet(MAX>>1);
+		primeList.set(0,primeList.size(),true);
+
+		int sqroot = (int) Math.sqrt(MAX);
+		primeList.clear(0);
+		for(int num = 3; num <= sqroot; num+=2)
+		{
+			if( primeList.get(num >> 1) )
+			{
+				int inc = num << 1;
+				for(int factor = num * num; factor < MAX; factor += inc)
+				{
+					//if( ((factor) & 1) == 1)
+					//{
+					primeList.clear(factor >> 1);
+					//}
+				}
+			}
+		}
+		//Sieve ends...
+
+		//Find Largest Truncatable Prime. (so we start from 1000000 - 1
+		int rightTrunc = -1, leftTrunc = -1;
+		for(int prime = (MAX - 1) | 1; prime >= 3; prime -= 2)
+		{
+			if(primeList.get(prime>>1))
+			{
+				//Already found Right Truncatable Prime?
+				if(rightTrunc == -1)
+				{
+					int right = prime;
+					while(right > 0 && right % 2 != 0 && primeList.get(right >> 1)) right /= 10;
+					if(right == 0) rightTrunc = prime;
+				}
+
+				//Already found Left Truncatable Prime?
+				if(leftTrunc == -1 )
+				{
+					//Left Truncation
+					String left = Integer.toString(prime);
+					if(!left.contains("0"))
+					{
+						while( left.length() > 0 ){
+							int iLeft = Integer.parseInt(left);
+							if(!primeList.get( iLeft >> 1)) break;
+							left = left.substring(1);
+						}
+						if(left.length() == 0) leftTrunc = prime;
+					}
+				}
+				if(leftTrunc != -1 && rightTrunc != -1) //Found both? then Stop loop
+				{
+					break;
+				}
+			}
+		}
+		System.out.println("Left  Truncatable : " + leftTrunc);
+		System.out.println("Right Truncatable : " + rightTrunc);
+	}
+}