package com.coding.basic.array;
public class ArrayUtil {
/**
* 给定一个整形数组a , 对该数组的值进行置换
例如: a = [7, 9 , 30, 3] , 置换后为 [3, 30, 9,7]
如果 a = [7, 9, 30, 3, 4] , 置换后为 [4,3, 30 , 9,7]
* @param origin
* @return
*/
public void reverseArray(int[] origin){
int length = origin.length;
int[] temp = new int[length];
for (int i = 0; i < length; i++) {
temp[i] = origin[length-1-i];
}
System.arraycopy(temp, 0, origin, 0, length);
}
/**
* 现在有如下的一个数组: int oldArr[]={1,3,4,5,0,0,6,6,0,5,4,7,6,7,0,5}
* 要求将以上数组中值为0的项去掉,将不为0的值存入一个新的数组,生成的新数组为:
* {1,3,4,5,6,6,5,4,7,6,7,5}
* @param oldArray
* @return
*/
public int[] removeZero(int[] oldArray){
int length = oldArray.length;
int[] tempArr = new int[length];
int j = 0;
int zeroNum = 0;//储存0的个数
for (int i = 0; i < length; i++) {
if(oldArray[i]!=0){
tempArr[j] = oldArray[i];
j ++;
}else{
zeroNum ++;
}
}
//删除数组尾端的0
int[] newArray = new int[length-zeroNum];
System.arraycopy(tempArr, 0, newArray, 0, length-zeroNum);
return newArray;
}
/**
* 给定两个已经排序好的整形数组, a1和a2 , 创建一个新的数组a3, 使得a3 包含a1和a2 的所有元素, 并且仍然是有序的
* 例如 a1 = [3, 5, 7,8] a2 = [4, 5, 6,7] 则 a3 为[3,4,5,6,7,8] , 注意: 已经消除了重复
* @param array1
* @param array2
* @return
*/
public int[] merge(int[] array1, int[] array2){
int length1 = array1.length;
int length2 = array2.length;
int[] array3 = new int[length1 + length2];
//将array1、array2的值加入array3中
System.arraycopy(array1, 0, array3, 0, length1);
System.arraycopy(array2, 0, array3, length1, length2);
int length = array3.length;
int temp;
//将array3冒泡排序
for (int i = 0; i < length; i++) {
for (int j = 0; j < length - i; j++) {
if(array3[i]>array3[j+i]){
temp = array3[i];
array3[i] = array3[j+i];
array3[j+i] = temp;
}
}
}
return duplicate(array3);
}
/**
*去重
*/
private int[] duplicate(int[] array){
for (int i = 1; i < array.length; i++) {
if(array[i-1]==array[i]){
array[i] = 0;
}
}
return removeZero(array);
}
/**
* 位图法合并
* @param array1
* @param array2
* @return
*/
public int[] merge2(int[] array1, int[] array2){
int bitSize = 0;
int a = array1[array1.length-1] ;
int b = array2[array2.length-1];
bitSize =(a>b)?a:b;
boolean[] bitmap = new boolean[bitSize+1];
for (int i = 0; i < array1.length; i++) {
bitmap[array1[i]]=true;
}
for (int i = 0; i < array2.length; i++) {
bitmap[array2[i]]=true;
}
ArrayList<Integer> ls = new ArrayList<>();
for (int i = 0; i < bitmap.length; i++) {
if(bitmap[i]==true){
ls.add(i);
}
}
return objList2int(ls);
}
/**
* 把一个已经存满数据的数组 oldArray的容量进行扩展, 扩展后的新数据大小为oldArray.length + size
* 注意,老数组的元素在新数组中需要保持
* 例如 oldArray = [2,3,6] , size = 3,则返回的新数组为
* [2,3,6,0,0,0]
* @param oldArray
* @param size
* @return
*/
public int[] grow(int [] oldArray, int size){
int[] newArray = new int[oldArray.length+size];
System.arraycopy(oldArray, 0,newArray , 0, oldArray.length);
return newArray;
}
/**
* 斐波那契数列为:1,1,2,3,5,8,13,21...... ,给定一个最大值, 返回小于该值的数列
* 例如, max = 15 , 则返回的数组应该为 [1,1,2,3,5,8,13]
* max = 1, 则返回空数组 []
* @param max
* @return
*/
public int[] fibonacci(int max){
int[] array = {};
if(max <= 1)return array;
//生成 斐波那契数列的ArrayList集合
ArrayList<Integer> ls = new ArrayList<>();
ls.add(1);ls.add(1);
int next;int i = 1;
while(true){
next = (int)ls.get(i) +(int)ls.get(i-1);
if(next >= max){
break;
}
ls.add(next);
i ++;
}
return objList2int(ls);
}
/**
* 返回小于给定最大值max的所有素数数组
* 例如max = 23, 返回的数组为[2,3,5,7,11,13,17,19]
* @param max
* @return
*/
public int[] getPrimes(int max){
ArrayList<Integer> primesList = new ArrayList<>();
boolean flag;
for (int i = 2; i < max; i++) {
flag = false;
for (int j = 2; j <= Math.sqrt(i); j++) {
if (i % j == 0) {
flag =true;
break;
}
}
if(!flag){
primesList.add(i);
}
}
return objList2int(primesList);
}
/**
* 所谓“完数”, 是指这个数恰好等于它的因子之和,例如6=1+2+3
* 给定一个最大值max, 返回一个数组, 数组中是小于max 的所有完数
* @param max
* @return
*/
public int[] getPerfectNumbers(int max){
int temp;
ArrayList<Integer> perfectList = new ArrayList<Integer>();
for (int i = 6; i <= max; i++) {
temp = 0;
for (int j = 1; j <= (i/2); j++) {
if(i%j == 0){
temp += j;
}
}
if(temp == i){
perfectList.add(i);
}
}
return objList2int(perfectList);
}
/**
* 用seperator 把数组 array给连接起来
* 例如array= [3,8,9], seperator = "-"
* 则返回值为"3-8-9"
* @param array
* @param s
* @return
*/
public String join(int[] array, String seperator){
StringBuilder str = new StringBuilder();
for (int i = 0; i < array.length; i++) {
str.append(array[i]+seperator);
}
return str.substring(0, str.lastIndexOf(seperator));
}
/**
* 将存储int数据的ArrayList转换为int数组
* @param ls
* @return
*/
public int[] objList2int(ArrayList<Integer> ls){
Object[] objArr = ls.toArray();
int[] array = new int[ls.size()];
for (int i = 0; i < ls.size(); i++) {
array[i] = (int) objArr[i];
}
return array;
}
}