黑马程序员——day04

来源：互联网发布：日本搞笑电影知乎编辑：程序博客网时间：2024/04/30 16:47

1，折半查找

class ArrayTest
{

public static void main(String[] arrgs)
{
int[] arr = {1,2,3,4,5,6,7,8,9};
int index = halfSearch_2(arr,7);
System.out.println("index="+index);
}

/*折半查找*/

public static int halfSearch_2(int[] arr,int key)
{
int min = 0,max = arr.length - 1,mid;
while(min<=max)
{
mid = (min+max)>>1;
if(key>arr[mid])
min = mid + 1;
else if(key<arr[mid])
max = min -1;
else
return mid;
}
return -1;
}

public static int halfSearch(int[] arr, int key)
{
int min,max,mid;
min = 0;
max = arr.length - 1;
mid = (min+max)/2;

while(arr[mid]!=key)
{
if(key>arr[mid])
min = mid + 1;

if(key<arr[mid])
max = mid - 1;
if(min>max)
return -1;

mid = (max+min)/2;
}
return mid;
}
}

******************************************************************************************************************************************************************

2,进制转换

class ArrayTest2
{

public static void main(String[] args)
{
//toBin(2);
toHex(60);
}

/*
十进制-->十六进制
*/
public static void toHex(int num)
{
StringBuffer sb = new StringBuffer();

for(int x=0; x<8;x++)
{
int temp = num & 15;
if(temp>9)
sb.append((char)(temp-10+'A'));
else
sb.append(temp);

num = num >>> 4;
}

System.out.println(sb.reverse());
}

/*
十进制-->二进制
*/
public static void toBin(int num)
{
StringBuffer sb = new StringBuffer();
while(num>0)
{
sb.append(num%2);
num = num>>>1;
}
System.out.println(sb.reverse());
}
}

******************************************************************************************************************************************************************

class ArrayTest3
{
//查表法
public static void main(String[] args)
{
//toHex(-60);
toBin(16);
}

public static void toBin(int num)
{
char[] chs ={'0','1'};

char[] arr = new char[32];
int pos = arr.length;

while(num!=0)
{
int temp = num & 1;
arr[--pos] = chs[temp];
num = num >>> 1;
}

for(int x = pos;x<arr.length;x++)
{
System.out.print(arr[x]);
}
System.out.println();
}

public static void toHex(int num)
{

char[] chs ={
'0','1','2','3'
,'4','5','6','7'
,'8','9','A','B'
,'C','D','E','F'
};
char[] arr = new char[8];
int pos = arr.length;
while(num!=0)
{
int temp = num & 15;

arr[--pos] = chs[temp];
num = num >>> 4;
}

for(int x=pos;x<arr.length;x++)
{
System.out.print(arr[x] + ",");
}
System.out.println();
}
}

******************************************************************************************************************************************************************

class ArrayTest4
{
public static void main(String[] args)
{

toBin(6);
toHex(60);
toBa(15);
}

//10-->2
public static void toBin(int num)
{
trans(num,1,1);
}
//10-->8
public static void toBa(int num)
{
trans(num,7,3);
}
//10-->16
public static void toHex(int num)
{
trans(num,15,4);
}

public static void trans(int num,int base,int offset)
{
if(num ==0)
{
System.out.println(0);
return;
}
char[] chs = {'0','1','2','3'
,'4','5','6','7'
,'8','9','A','B'
,'C','D','E','F'};
char[] arr = new char[32];
int pos = arr.length;

while(num!=0)
{
int temp = num & base;
arr[--pos] = chs[temp];
num = num >>> offset;
}

for(int x=pos;x<arr.length;x++)
{
System.out.print(arr[x]);
}
System.out.println();
}
}