package com.coderising.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 i = 0;
while (i < origin.length - 1 - i) {
int temp = origin[origin.length - 1 - i];
origin[origin.length - 1 - i] = origin[i];
origin[i] = temp;
i++;
}
}
/**
* 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 point = 0;
for (int i : oldArray) {
if (i != 0) {
oldArray[point++] = i;
}
}
int[] newArray = new int[point];
System.arraycopy(oldArray, 0, newArray, 0, point);
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) {
//两个指针
int pos1 = 0;
int pos2 = 0;
int point = 0;
int[] newArray = new int[array1.length + array2.length];
while (pos1 < array1.length && pos2 < array2.length) {
if (array1[pos1] > array2[pos2]) {
newArray[point++] = array2[pos2++];
} else if (array1[pos1] < array2[pos2]) {
newArray[point++] = array1[pos1++];
} else {
newArray[point++] = array1[pos1++];
pos2++;
}
}
while (pos1 < array1.length) {
newArray[point++] = array1[pos1++];
}
while (pos1 < array2.length) {
newArray[point++] = array1[pos2++];
}
int[] array = new int[point];
System.arraycopy(newArray, 0, array, 0, point);
return array;
}
/**
* 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 a = 0;
int b = 1;
int[] array = new int[max];
int i = 0;
if (max >= 2) {
array[i++] = 1;
}
while (a + b < max) {
int temp = b;
b = a + b;
a = temp;
array[i++] = b;
}
int[] newArray = new int[i];
System.arraycopy(array, 0, newArray, 0, i);
return newArray;
}
/**
* 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[] array = new int[max / 2 + 1];
int pos = 0;
for (int i = 1; i < max; i++) {
if (prime(i)) {
array[pos++] = i;
}
}
int[] newArray = new int[pos];
System.arraycopy(array, 0, newArray, 0, pos);
return newArray;
}
private boolean prime(int value) {
if (value < 2) {
return false;
} else if (value == 2) {
return true;
} else {
for (int i = 2; i < value / 2 + 1; i++) {
if (value % 2 == 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 pos = 0;
int[] array = new int[max];
for (int i = 1; i < max; i++) {
if (perfectNumber(i)) {
array[pos++] = i;
}
}
int[] newArray = new int[pos];
System.arraycopy(array, 0, newArray, 0, pos);
return newArray;
}
private boolean perfectNumber(int value) {
if (value == 1 || prime(value)) {
return false;
} else {
int sum = 0;
for (int i = 1; i <= value / 2; i++) {
if (value % i == 0) {
sum += i;
}
}
if (sum == value) {
return true;
}
return false;
}
}
/**
* 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) {
String out = "";
for (int i = 0; i < array.length; i++) {
if (i == 0) {
out += String.valueOf(i);
} else {
out += seperator + String.valueOf(i);
}
}
return out;
}
public static void main(String[] args) {
ArrayUtil arrayUtil = new ArrayUtil();
//reverse
int[] a = {7, 9, 30, 3};
arrayUtil.reverseArray(a);
System.out.println(a);
//remove zero
int[] zero = {1, 3, 4, 5, 0, 0, 6, 6, 0, 5, 4, 7, 6, 7, 0, 5};
int[] afterZero = arrayUtil.removeZero(zero);
System.out.println(afterZero);
//merge
int[] a1 = {3, 5, 7, 8};
int[] a2 = {4, 5, 6, 7};
int[] merge = arrayUtil.merge(a1, a2);
System.out.println(merge);
//grow
int[] oldArray = {2, 3, 6};
int[] grow = arrayUtil.grow(oldArray, 3);
System.out.println(grow);
//fibonacci
int[] fibonacci = arrayUtil.fibonacci(2);
System.out.println(fibonacci);
//primes
int[] primes = arrayUtil.getPrimes(15);
System.out.println(primes);
//perfect
int[] perfect = arrayUtil.getPerfectNumbers(500);
System.out.println(perfect);
//join
int[] joinArray = {2};
String join = arrayUtil.join(joinArray, "-");
System.out.println(join);
}
}