算法导论exercise 5.1-2

#include <iostream>
#include <cstdlib>
#include <time.h>
using namespace std;

int random(int a , int b)
{
    int p,m=1;               //m用来保存2^p
    for(p=0 ; m-1<b-a ; p++) //p是二进制位数
    {
        m *= 2;              //再用m保存十进制的值
    }

    m = rand()%2;

    for(int i=0 ; i<p-1 ; i++)
    {
        m = m*2+rand()%2;
    }

    if(m > b-a)
    {
        return random(a , b);
    }
    else
    {
        return m+a;
    }
}
int main()
{
    int a,b;
    cin >> a >>b;//输入3和7
    srand(time (0) );
    int m;
    int three , four , five ,
        six , seven;//这几个变量用来统计3,4,5,6,7出现次数
    three = four = five =
        six = seven=0;
    for(int i=0 ; i<1000 ; i++)
    {
        m = random(a , b);
        cout << m << endl;
        switch(m)
        {
            case 3:
            three++;break;
            case 4:
            four++;break;
            case 5:
            five++;break;
            case 6:
            six++;break;
            case 7:
            seven++;
            default:break;
        }
    }
    cout << three << ' ' << four
    << ' ' << five << ' ' << six << ' ' <<seven;

    return 0;
}