Consider the following algorithm to generate a sequence of numbers. Start with an integer n. If n is even, divide by 2. If n is odd, multiply by 3 and add 1. Repeat this process with the new value of n, terminating when n = 1. For example, the following sequence of numbers will be generated for n = 22:
For an input n, the cycle-length of n is the number of numbers generated up to and including the 1. In the example above, the cycle length of 22 is 16. Given any two numbers i and j, you are to determine the maximum cycle length over all numbers between i and j, including both endpoints.
1 10 100 200 201 210 900 1000
1 10 20 100 200 125 201 210 89 900 1000 174
*** my Java solution
import java.io.BufferedReader; import java.io.InputStreamReader; public class Main { final static BufferedReader reader_ = new BufferedReader(new InputStreamReader(System.in)); /** * @param args */ public static void main(String[] args) { new Problem().run(); } static String[] ReadLn() { String[] tokens = null; try { String line = reader_.readLine(); String REGEX_WHITESPACE = "\\s+"; String cleanLine = line.trim().replaceAll(REGEX_WHITESPACE, " "); tokens = cleanLine.split(REGEX_WHITESPACE); } catch (Exception e) {} return tokens; } } class Problem implements Runnable { long CACHE_SIZE = 65536; private final long[] cache_ = new long[(int) CACHE_SIZE]; /** * Compute cycle length for a single number * * @param n number for which we find cycle length * @return cycle length */ long cycleLen(long n) { long len = 1; if (n != 1) { len = getFromCache(n); if (len == 0) { //not yet in cache // Recursively compute and store all intermediate values of cycle length if ((n & 1) == 0) { len = 1 + cycleLen(n >> 1); } else { len = 1 + cycleLen(n * 3 + 1); } putInCache(n, len); } } return len; } void putInCache(long n, long len) { if(n < CACHE_SIZE) { cache_[(int)n] = len; } } long getFromCache(long n) { long result = 0; if(n < CACHE_SIZE) { result = cache_[(int)n]; } return result; } /** * Find max cycle on interval * * @param from interval start * @param to interval end * @return max cycle */ Long maxCycle(Long from, Long to) { Long result = 0L; Long cycle = 0L; // Get all values of cycle length on the interval and put these values into a sorted set for (long i = from; i <= to; i++) { cycle = cycleLen(i); if (cycle > result) result = cycle; } return result; } public void run() { String[] tokens = null; long from, to, result = 0; long arg1, arg2 = 0; while ((tokens = Main.ReadLn()) != null) { if (tokens.length == 2) { arg1 = new Long(tokens[0]).longValue(); arg2 = new Long(tokens[1]).longValue(); from = (arg1 <= arg2) ? arg1 : arg2; to = (arg2 >= arg1 ) ? arg2 : arg1; result = maxCycle(from, to); out(arg1+" "+arg2+" "+result); } } } static void out(String msg) { System.out.println(msg); } }