First power of 2 that has leading decimal digits of 12: Difference between revisions

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 Took 1.422321658s
+</pre>
+=={{header|Java}}==
+<lang java>
+public class FirstPowerOfTwo {
+    public static void main(String[] args) {
+        runTest(12, 1);
+        runTest(12, 2);
+        runTest(123, 45);
+        runTest(123, 12345);
+        runTest(123, 678910);
+    }
+    private static void runTest(int l, int n) {
+        System.out.printf("p(%d, %d) = %,d%n", l, n, p(l, n));
+    }
+    public static int p(int l, int n) {
+        int test = 0;
+        double log = Math.log(2) / Math.log(10);
+        int factor = 1;
+        int loop = l;
+        while ( loop > 10 ) {
+            factor *= 10;
+            loop /= 10;
+        }
+        while ( n > 0) {
+            test++;
+            int val = (int) (factor * Math.pow(10, test * log % 1));
+            if ( val == l ) {
+                n--;
+            }
+        }
+        return test;
+    }
+}
+</lang>
+{{out}}
+<pre>
+p(12, 1) = 7
+p(12, 2) = 80
+p(123, 45) = 12,710
+p(123, 12345) = 3,510,491
+p(123, 678910) = 193,060,223
 </pre>