package week2_0305.array;
import java.util.ArrayList;
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) {
throw new IllegalArgumentException();
}
int temp = 0;
for (int i = 0; i< origin.length/2; i++) {
temp = origin[i];
origin[i] = origin[origin.length - i];
origin[origin.length - 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) {
throw new IllegalArgumentException();
}
int[] newArray = new int[oldArray.length];
int index = 0;
for (int i =0; i < oldArray.length; i ++){
if (oldArray[i] == 0) {
continue;
} else {
newArray[index++] = oldArray[i];
}
}
return 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) {
throw new IllegalArgumentException();
}
int[] array3 = new int[array1.length + array2.length];
int index1 = 0;
int index2 = 0;
int actualSize = 0;
for (int i = 0; i < array3.length; i ++) {
//把array2剩余的部分拷入数据
if (index1 >= array1.length) {
arrayCopy(array2, index2, array3, i, array2.length - index2);
actualSize = i + array2.length - index2;
return copyOf(array3, actualSize);
}
if (index2 >= array2.length) {
arrayCopy(array1, index1, array3, i, array1.length - index1);
actualSize = i + array1.length - index1;
return copyOf(array3, actualSize);
}
if (array1[index1] < array2[index2]) {
array3[i] = array1[index1];
index1 ++;
} else if (array1[index1] == array2[index2]) {
array3[i] = array1[index1];
index1 ++;
index2 ++;
} else {
array3[i] = array2[index2];
index2 ++;
}
}
// array1 he array2 均为 空数组的情况
return new int[0];
}
private void arrayCopy(int[] src, int srcPos, int[] dest, int destPos, int length) {
for (int i = 0; i< length; i++) {
dest[destPos++] = src[srcPos++];
}
}
private int[] copyOf(int[] arr, int size) {
int[] dest = new int[size];
for (int i = 0; i< size; i++) {
dest[i] = arr[i];
}
return dest;
}
/**
* 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 || size <0) {
throw new IllegalArgumentException();
}
int[] newArray = new int[oldArray.length + size];
for (int i = 0; i < oldArray.length; i++) {
newArray[i] = oldArray[i];
}
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){
if (max < 0 ) {
throw new IllegalArgumentException();
} else if (max == 1) {
return new int[0];
}
ArrayList<Integer> list = new ArrayList<Integer>();
list.add(1);
list.add(1);
int i = 0;
while(true) {
int num = (int)list.get(i) + (int)list.get(i+1);
if (num < max) {
list.add(num);
} else {
break;
}
}
return listToArray(list);
}
private int[] listToArray(ArrayList<Integer> list){
int[] arr = new int[list.size()];
for (int i = 0;i < list.size(); i++) {
arr[i] = (int)list.get(i);
}
return arr;
}
/**
* 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){
if (max <2) {
throw new IllegalArgumentException();
}
ArrayList<Integer> list = new ArrayList<Integer>();
for (int i = 2; i < max; i++) {
if (isPrime(i)) {
list.add(i);
}
}
return listToArray(list);
}
public boolean isPrime(int m) {
for (int i = 1; i < m/2; i++) {
if (m % 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){
if (max < 0) {
throw new IllegalArgumentException();
}
ArrayList<Integer> list = new ArrayList<Integer>();
for (int i = 0; i< max; i++) {
if (isPerfectNumber(i)) {
list.add(i);
}
}
return listToArray(list);
}
public boolean isPerfectNumber(int num) {
int sum = 0;
for (int i = 0; i < num; i++) {
if (num % i == 0) {
sum += i;
}
}
if (sum == num) {
return true;
} else {
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 s
* @return
*/
public String join(int[] array, String seperator){
if (array == null) {
throw new IllegalArgumentException();
}
StringBuilder builder = new StringBuilder();
for (int i = 0; i < array.length; i++) {
builder.append(array[i]).append(seperator);
}
return builder.substring(0, builder.length() - seperator.length());
}
}