package com.util_1;
import java.util.*;
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[] oldArr = origin;
int newLength = oldArr.length;
int[] newArr = new int[newLength];
for (int i = 0; i < newLength; i++) {
newArr[newLength - i - 1] = oldArr[i];
}
for (int s : newArr) {
System.out.println(s);
}
}
/**
* 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[] oldArr = oldArray;
int oldLength = oldArr.length;
int[] newArr = new int[oldLength];
int index = 0;
int zeroCount = 0;
for (int i = 0; i < oldLength; i++) {
if (oldArr[i] == 0) {
zeroCount++;
} else {
newArr[index++] = oldArr[i];
}
}
int[] newArrs = Arrays.copyOf(newArr, index);
return newArrs;
}
/**
* 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 newLength = array1.length + array2.length;
int[] newArr = new int[newLength];
int index = 0;
for (int i = 0; i < array1.length; i++) {
newArr[index++] = array1[i];
}
for (int i = 0; i < array2.length; i++) {
newArr[index++] = array2[i];
}
//冒泡排序
for (int i = 0; i < newArr.length; i++) {
for (int j = i + 1; j < newArr.length; j++) {
if (newArr[i] > newArr[j]) {
int temp = newArr[i];
newArr[i] = newArr[j];
newArr[j] = temp;
}
}
}
//数组去重
boolean[] b = new boolean[newArr.length];
int counts = newArr.length;
for (int i = 0; i < newArr.length; i++) {
for (int j = i + 1; j < newArr.length; j++) {
if (newArr[i] == newArr[j] && b[i] == false) {
b[j] = true;
counts--;
}
}
}
int[] result = new int[counts];
int j = 0;
for (int i = 0; i < newArr.length; i++) {
if (b[i] == false) {
result[j] = newArr[i];
j++;
}
}
return result;
}
/**
* 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 oldLength = oldArray.length;
int newLength = oldLength + size;
int[] result = Arrays.copyOf(oldArray, newLength);
return result;
}
/**
* 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 = 1, b = 1, c = 2;
int[] arr = new int[max + 1];
int i = 2;
if (max == 1) {
return Arrays.copyOf(arr, 0);
} else if (max <= 0) {
throw new IllegalArgumentException("不能输入<=0的参数：" + max);
} else {
arr[0] = 1;
arr[1] = 1;
do {
c = a + b;
a = b;
b = c;
arr[i++] = c;
} while (c < max);
}
if (arr[i - 1] >= max) {
return Arrays.copyOf(arr, i - 1);
}
return Arrays.copyOf(arr, i);
}
/**
* 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) {
class IsPrime {
// 判断某整数是否为素数
public boolean isPrimes(int n) {
if (n < 2) {
return false;
}
for (int i = 2; i * i <= n; i++) {
if (n % i == 0) {
return false;
}
}
return true;
}
}
List list = new ArrayList();
IsPrime isPrime = new IsPrime();
for (int i = 2; i < max; i++) {
if (isPrime.isPrimes(i)) {
list.add(i);
}
}
int[] arr = new int[list.size()];
for (int i = 0; i < list.size(); i++) {
arr[i] = (int) list.get(i);
}
return arr;
}
/**
* 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) {
//保存每组的分解因子
List list = new ArrayList();
List pm = new ArrayList();
int sum = 0;
//除数
for (int i = 2; i < max; i++) {
//被除数
sum=0;
for (int j = 1; j < i / 2 + 1; j++) {
if (i % j == 0) {
list.add(j);
sum += j;
}
}
if (sum == i) {
pm.add(i);
}
list.clear();
}
int[] pmaArr = new int[pm.size()];
for (int i = 0; i < pm.size(); i++) {
pmaArr[i] = (int) pm.get(i);
}
return pmaArr;
}
/**
* 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
* @return
*/
public String join(int[] array, String seperator) {
String s = new String();
for (int i = 0; i < array.length; i++) {
if (i < array.length - 1) {
s += array[i] + seperator;
} else {
s += array[i];
}
}
return s;
}
}