java实现位图算法

来源：互联网发布：数据治理体系框架编辑：程序博客网时间：2024/05/01 05:22

1、利用java自带的BitSet来

package lpc.Algorithm;

import java.util.BitSet;

public class BitMap {

public static void main(String[] args) {

// TODO Auto-generated method stub

int count = 100000000;

BitSet bit = new BitSet(count);

int i = 1000;

while(i>0){

bit.set((int)(Math.random()*count));

i--;

}

for (int index = 0; index < count; index++) {

if(bit.get(index)){

System.out.println(index+",");

}

System.out.println("end");

}

2、必行编写My_BitSet类

package lpc.Algorithm;

public class My_BitSet {

private int[] mBits;

public int[] getmBits() {

return mBits;

}

private int mSize;

/**

* 构造函数

* @param size 初始化mBits 的长度

public My_BitSet(int size) {

// TODO Auto-generated constructor stub

mSize = size;

initBits();

}

//初始化整形数组

private void initBits() {

// TODO Auto-generated method stub

int count = (int) Math.ceil(mSize/32f)+1;

mBits =new int[count];

}

/**

* 将制定bit位置设置为1

* @param pos

public void set(int pos){

//得到此pos在myits中的位置

//int index = (int)Math.floor(pos/32f);

int index = pos >> 5;

//把当前整数的地n位设置为1

//mBits[index] = mBits[index] | (1<<(pos%32));

mBits[index] = mBits[index] | (1<<(pos & 0x1F));

}

/**

* 获取指定位置是否存在

* @param pos

* @return

public boolean get(int pos){

//int index = (int)Math.floor(pos/32f);

int index = pos >> 5;

//return mBits[index] == (mBits[index] | 1 <<(pos%32));

return mBits[index] == (mBits[index] | 1 <<(pos & 0x1F));

}

public void reset(int pos){

int index = (int)Math.floor(pos/32f);

//把当前整数的第n位设置为0

mBits[index] = mBits[index] & ~(1<<(pos%32));

}

/**

* 清空，全部置0

* @param args

public void clear(){

int len = mBits.length;

for (int index = 0; index < len; index++) {

mBits[index] = 0 ;

}

public static void main(String[] args) {

//int[] a=new int[]{509,9,8,300,6,5,4,3,2,1,0};

int N=100000000;

int[] a=new int[N];

for (int i = 0; i < a.length; i++) {

a[i]=N-i-1;

}

int max=a[0];

for (int i : a) {

if (i>max) {

max=i;

}

long start = System.currentTimeMillis();

My_BitSet bitSet = new My_BitSet(max);

//设置值

for (int i : a) {

bitSet.set(i);

}

for (int i=0 ; i<=max; i++) {

if(bitSet.get(i)){};//防止刷屏只判断，什么也不做

}

long end = System.currentTimeMillis();

System.out.format("usetime: %d ms",(end-start));

System.out.println("----------打印原数组----------");

for (int i : a) {

if(bitSet.get(i)){

System.out.println(i);

}

System.out.println("---------打印排序后数组-------------");

for (int i=0 ; i<=max; i++) {

if(bitSet.get(i)){

System.out.println(i);

}

测试结果

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