The 3n + 1 problem

     Problems in Computer Science are often classified as belonging to a certain class of problems (e.g., NP, Unsolvable, Recursive). In this problem you will be analyzing a property of an algorithm whose classification is not known for all possible inputs.    Consider the following algorithm:        1.      input n        2.      print n        3.      if n = 1 then STOP        4.           if n is odd then n <- 3n + 1        5.           else n <- n / 2        6.      GOTO 2    Given the input 22, the following sequence of numbers will be printed 22 11 34 17 52 26 13 40 20 10 5 16 8 4 2 1    It is conjectured that the algorithm above will terminate (when a 1 is printed) for any integral input value. Despite the simplicity of the algorithm, it is unknown whether this conjecture is true. It has been verified, however, for all integers n such that 0 < n < 1,000,000 (and, in fact, for many more numbers than this.)    Given an input n, it is possible to determine the number of numbers printed (including the 1). For a given n this is called the cycle-length of n. In the example above, the cycle length of 22 is 16.    For any two numbers i and j you are to determine the maximum cycle length over all numbers between i and j.Input    The input will consist of a series of pairs of integers i and j, one pair of integers per line. All integers will be less than 1,000,000 and greater than 0.    You should process all pairs of integers and for each pair determine the maximum cycle length over all integers between and including i and j.    You can assume that no opperation overflows a 32-bit integer.Output    For each pair of input integers i and j you should output i, j, and the maximum cycle length for integers between and including i and j. These three numbers should be separated by at least one space with all three numbers on one line and with one line of output for each line of input. The integers i and j must appear in the output in the same order in which they appeared in the input and should be followed by the maximum cycle length (on the same line).Sample Input    1 10    100 200    201 210    900 1000Sample Output    1 10 20    100 200 125    201 210 89    900 1000 174

看到英文的题目头都疼。。。。

这道题大意就是给你两个数，在这两个数的范围内有一个数，这个数拥有最大周期长度，输出这个最大周期长度。

要注意这两个数，题目也没说这两个数必须第二个大于第一个数。

#include<stdio.h>#include<iostream>using namespace std;int main(){int m,n,t,max,i;while(scanf("%d%d",&m,&n)!=EOF){printf("%d %d ",m,n);if(m>n){t=m;m=n;n=t;}for(i=m;i<=n;i++){int n=i,sum=1;while(n-1){if(n%2)n=3*n+1;elsen=n/2;sum++;}if(sum>max)max=sum;}printf("%d\n",max);}return 0;}