package week2.array;
import java.util.Arrays;
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 (origin == null) {
return;
}
int len = origin.length;
int forLen = len / 2;
int temp;
for (int i = 0; i < forLen; i++) {
temp = origin[i];
origin[i] = origin[len - 1 - i];
origin[len - 1 - i] = temp;
}
}
/**
* 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) {
if (oldArray == null) {
return null;
}
int[] newArray = new int[oldArray.length];
int index = 0;
for (int x : oldArray) {
if (x != 0) {
newArray[index] = x;
index++;
}
}
return Arrays.copyOf(newArray, index);
}
/**
* 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) {
if (array1 == null && array2 == null) {
return null;
} else if (array1 == null) {
return array2;
} else if (array2 == null) {
return array1;
}
int[] newArray = new int[array1.length + array2.length];
int newIndex = 0;
int index1 = 0;
int index2 = 0;
int len1 = array1.length;
int len2 = array2.length;
int x;
int y;
while (index1 < len1 && index2 < len2) {
x = array1[index1];
y = array2[index2];
if (x < y) {
newArray[newIndex] = x;
index1++;
} else if (x == y) {
newArray[newIndex] = x;
index1++;
index2++;
} else {
newArray[newIndex] = y;
index2++;
}
newIndex++;
}
for (int i = index1; i < len1; i++) {
newArray[newIndex] = array1[i];
newIndex++;
}
for (int i = index2; i < len2; i++) {
newArray[newIndex] = array2[i];
newIndex++;
}
return Arrays.copyOf(newArray, newIndex);
}
/**
* 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) {
if (oldArray == null) {
return null;
}
if (size < 0) {
size = 0;
}
return Arrays.copyOf(oldArray, oldArray.length + size);
}
/**
* 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) {
if (max <= 1) {
return null;
}
int now = 2;
int index = 1;
int[] fiboArray = new int[] { 1, 1 };
while (now < max) {
now = fiboArray[index] + fiboArray[index - 1];
if (index + 2 > fiboArray.length) {
fiboArray = Arrays.copyOf(fiboArray, fiboArray.length * 2);
}
fiboArray[++index] = now;
}
return Arrays.copyOf(fiboArray, index);
}
/**
* 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
* @throws Exception
*/
public int[] getPrimes(int max) throws Exception {
if (max < 2) {
return null;
}
int[] primes = new int[] { 2 };
int index = 0;
int newPrimes = 3;
while (newPrimes < max) {
if (index + 2 > primes.length) {
primes = Arrays.copyOf(primes, primes.length * 2);
}
primes[++index] = newPrimes;
boolean foundPrime = false;
while (!foundPrime) {
newPrimes += 2;
foundPrime = true;
int mid = newPrimes / 2 + 1;
for (int i = 3; i <= mid; i++) {
if (newPrimes % i == 0) {
foundPrime = false;
break;
}
}
}
}
return Arrays.copyOf(primes, ++index);
}
/**
* 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 perfectNumber = 6;
if (max < perfectNumber) {
return null;
}
int[] perfectNumbers = new int[] { perfectNumber };
while (perfectNumber < max) {
perfectNumber++;
int sum = 0;
for (int i = 1; i < perfectNumber; i++) {
if (perfectNumber % i == 0) {
sum += i;
}
}
if (sum == perfectNumber) {
int[] newArr = new int[perfectNumbers.length + 1];
System.arraycopy(perfectNumbers, 0, newArr, 0, perfectNumbers.length);
perfectNumbers = newArr;
perfectNumbers[perfectNumbers.length - 1] = perfectNumber;
}
}
return perfectNumbers;
}
/**
* 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) {
if (array == null || array.length == 0) {
return null;
}
StringBuilder sb = new StringBuilder();
sb.append(array[0]);
for (int i = 1; i < array.length; i++) {
sb.append(seperator + array[i]);
}
return sb.toString();
}
}