The 3n + 1 problem（C语言）

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 1000

Sample Output
1 10 20
100 200 125
201 210 89
900 1000 174
思路：可以将算法设计为一个函数，利用循环求出最大循环周期，最后输出。

#include<stdio.h>
int main()
{
	int ying(int n);
	int n,m;
	while(scanf("%d %d",&n,&m)!=EOF)
	{		
		int i,num=0,min,max;
		if(n>m)
		{max=n;min=m;}
		else
		{max=m;min=n;}
		for(i=min;i<=max;i++)
		{
			if(num<ying(i))
			num=ying(i);
		}
		printf("%d %d %d\n",n,m,num);
	}
	return 0;
}
int ying(int n)
{
	int cnt=1;
	while(1)
	{
		if(n==1)
		return cnt;
		else if(n%2!=0)
		n=3*n+1;
		else
		n=n/2;
		cnt++;
	}
}

这道题卡了我好多次，主要是卡在
1.没有注意i和j的大小，不是样例是i小j大，就默认为是那样。
2.int i,num=0,min,max;这一行应该在while循环里，因为每次输入时num的值应为0。
总之挺简单的一题，但不注意细节就会很难受。