Uva 3n+1 问题

水深无声 2022-06-12 10:16 138阅读 0赞

### 3n+1 问题: ###

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 before and including
    the 1 is printed. 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 and including both 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 10,000 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 operation 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 1000
    Sample Output
    1 10 20
    100 200 125
    201 210 89
    900 1000 174

#include<stdio.h>
    int main ()
    {
        int i,j,n,m,k,b,c,f,t;
        while(scanf("%d%d",&i,&j)!=EOF)
        {
             c=0;
             f=0;
             if(i>j)
             {
    
                 t=i;
                 i=j;
                 j=t;
                 f=1;
             }
            for(k=i; k<=j; k++)
            {
                n=1;
                b=k;
                while(b!=1)
                {
                    if(b%2!=0)
                    {
                        b=b*3+1;
                    }
                    else
                        b=b/2;
                    n++;
                }
               if(c<n)
                c=n;
            }
            if(f==0)
            printf("%d %d %d\n",i,j,c);
            else
                printf("%d %d %d\n",j,i,c);
        }
        return 0;
    }

#### —-2017/7/21 ####

#### 总结：由于习惯性的思维认为i < j,导致错误。 ####