2013
11-10

# Uniform Generator

Computer simulations often require random numbers. One way to generate pseudo-random numbers is via a function of the form
     seed(x+1) = [ seed(x) + STEP ] % MOD

where "%" is the modulus operator.

Such a function will generate pseudo-random numbers (seed) between 0 and MOD-1. One problem with functions of this form is that they will always generate the same pattern over and over. In order to minimize this effect, selecting the STEP and MOD values carefully can result in a uniform distribution of all values between (and including) 0 and MOD-1.

For example, if STEP=3 and MOD=5, the function will generate the series of pseudo-random numbers 0, 3, 1, 4, 2 in a repeating cycle. In this example, all of the numbers between and including 0 and MOD-1 will be generated every MOD iterations of the function. Note that by the nature of the function to generate the same seed(x+1) every time seed(x) occurs means that if a function will generate all the numbers between 0 and MOD-1, it will generate pseudo-random numbers uniformly with every MOD iterations.

If STEP = 15 and MOD = 20, the function generates the series 0, 15, 10, 5 (or any other repeating series if the initial seed is other than 0). This is a poor selection of STEP and MOD because no initial seed will generate all of the numbers from 0 and MOD-1.

Your program will determine if choices of STEP and MOD will generate a uniform distribution of pseudo-random numbers.

Each line of input will contain a pair of integers for STEP and MOD in that order (1<=STEP,MOD<=100000).

For each line of input, your program should print the STEP value right-justified in columns 1 through 10, the MOD value right-justified in columns 11 through 20 and either “Good Choice” or “Bad Choice” left-justified starting in column 25. The “Good Choice” message should be printed when the selection of STEP and MOD will generate all the numbers between and including 0 and MOD-1 when MOD numbers are generated. Otherwise, your program should print the message “Bad Choice”. After each output test set, your program should print exactly one blank line.

3 5
15 20
63923 99999


         3         5    Good Choice

63923     99999    Good Choice


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import java.util.Scanner;
public class Main {

public static void main(String[] args) {
Scanner scan=new Scanner(System.in);
int s=0,m=0,ac=0;
boolean[] bands;
boolean flaj;
while(scan.hasNext()){
s=scan.nextInt();
m=scan.nextInt();
bands=new boolean[m+1];
flaj=true;
ac=0;
for(int i=0;i< m;i++){
if(bands[ac]){
flaj=false;
break;
}
bands[ac]=true;
ac+=s;
ac=ac%m;
}
ac=10-(s+"").length();
for(int i=0;i< ac;i++)System.out.print(" ");
System.out.print(s);
ac=10-(m+"").length();
for(int i=0;i< ac;i++)System.out.print(" ");
if (flaj) System.out.print(m+"    Good Choice\n\n");
}
}
}

1. 有一点问题。。后面动态规划的程序中
int dp[n+1][W+1];
会报错 提示表达式必须含有常量值。该怎么修改呢。。

2. 算法是程序的灵魂，算法分简单和复杂，如果不搞大数据类，程序员了解一下简单点的算法也是可以的，但是会算法的一定要会编程才行，程序员不一定要会算法，利于自己项目需要的可以简单了解。

3. int half(int *array,int len,int key)
{
int l=0,r=len;
while(l<r)
{
int m=(l+r)>>1;
if(key>array )l=m+1;
else if(key<array )r=m;
else return m;
}
return -1;
}
这种就能避免一些Bug
l,m,r
左边是l,m;右边就是m+1,r;