package com.java.xiaoqin.array;
import java.util.Objects;
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) {
if (null != origin) {
int[] temp = new int[origin.length];
System.arraycopy(origin, 0, temp, 0, origin.length);
for (int index = origin.length; index > 0; index--) {
origin[origin.length - index] = temp[index - 1];
}
}
}
/**
* 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 size = 0;
int[] newArray = new int[oldArray.length];
for (int indexO = 0; indexO < oldArray.length; indexO++) {
if (0 == oldArray[indexO]) {
continue;
}
newArray[size++] = oldArray[indexO];
}
int[] returnArray = new int[size];
System.arraycopy(newArray, 0, returnArray, 0, returnArray.length);
return returnArray;
}
/**
* 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[] mergeArray = new int[array1.length + array2.length];
int size = 0;
for (int index = 0, max = Math.max(array1.length, array2.length); index < max; index++) {
Object arrObj1 = null;
Object arrObj2 = null;
if (index < array1.length) {
arrObj1 = array1[index];
}
if (index < array2.length) {
arrObj2 = array2[index];
}
if (null != arrObj1 && Objects.equals(arrObj1, arrObj2)) {
arrObj2 = null;
}
for (int indexMerge = 0; indexMerge < size; indexMerge++) {
if (Objects.equals(arrObj1, mergeArray[indexMerge])) {
arrObj1 = null;
}
if (Objects.equals(arrObj2, mergeArray[indexMerge])) {
arrObj2 = null;
break;
}
}
if (null != arrObj1 && null != arrObj2 && (int) arrObj1 > (int) arrObj2) {
arrObj1 = (int) arrObj1 + (int) arrObj2;
arrObj2 = (int) arrObj1 - (int) arrObj2;
arrObj1 = (int) arrObj1 - (int) arrObj2;
}
if (null != arrObj1) {
mergeArray[size++] = (int) arrObj1;
}
if (null != arrObj2) {
mergeArray[size++] = (int) arrObj2;
}
}
int[] resultArr = new int[size];
System.arraycopy(mergeArray, 0, resultArr, 0, size);
return resultArr;
}
/**
* 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];
for (int indexOld = 0; indexOld < oldArray.length; indexOld++) {
newArray[indexOld] = oldArray[indexOld];
}
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[] newArray = new int[0];
if (max > 1) {
int size = 0;
newArray = new int[max];
if (max >= 1) {
for (int n = 1; n < Integer.MAX_VALUE; n++) {
int fibonacci = mFibonacci(n);
if (fibonacci < max) {
newArray[size++] = fibonacci;
} else {
break;
}
}
}
int[] resultArr = new int[size];
System.arraycopy(newArray, 0, resultArr, 0, size);
newArray = resultArr;
}
return newArray;
}
private int mFibonacci(int n) {
if (n == 0) return 0;
else if (n == 1) return 1;
else return mFibonacci(n - 1) + mFibonacci(n - 2);
}
/**
* 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) {
int[] newArray = new int[max];
int size = 0;
for (int index = 2; index < max; index++) {
if (isPrimes(index)) {
newArray[size++] = index;
}
}
int[] resultArr = new int[size];
System.arraycopy(newArray, 0, resultArr, 0, size);
return resultArr;
}
private boolean isPrimes(int number) {
int i = 1;
while (++i < number) {
if (number % i == 0) {
return false;
}
}
return true;
}
/**
* 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[] newArray = new int[max];
int size = 0;
for (int i = 6; i < max; i++) {
int total = 0;
for (int index = 1, length = i / 2; index <= length; index++) {
if (i % index == 0) {
total += index;
}
}
if (i == total) {
newArray[size++] = i;
}
}
int[] resultArr = new int[size];
System.arraycopy(newArray, 0, resultArr, 0, size);
return resultArr;
}
/**
* 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 seperator
* @return
*/
public String join(int[] array, String seperator) {
StringBuilder arrBuilder = new StringBuilder();
for (int arr : array) {
if (arrBuilder.length() > 0) {
arrBuilder.append(seperator);
}
arrBuilder.append(arr);
}
return arrBuilder.toString();
}
}