package datastructure.array;
import datastructure.List;
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;
for (int i = 0; i < origin.length / 2; i++) {
temp = origin[i];
origin[i] = origin[origin.length - 1 - i];
origin[origin.length - 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) {
throw new IllegalArgumentException();
}
int[] noZeroArray = new int[oldArray.length];
int index = 0;
for (int i = 0; i < oldArray.length; i++) {
if (oldArray[i] != 0) {
noZeroArray[index++] = oldArray[i];
}
}
return copyOf(noZeroArray, 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 indexOfArray1 = 0;
int indexOfArray2 = 0;
int totalLength = array1.length + array2.length;
int[] destArr = new int[totalLength];
for (int i = 0; i < totalLength; i++) {
if (indexOfArray1 >= array1.length) {
// array1填充完毕,将array2填充剩下的元素
arrayCopy(array2, indexOfArray2, destArr, i, array2.length - indexOfArray2);
int actualSize = i + array2.length - indexOfArray2;
return copyOf(destArr, actualSize);
}
if (indexOfArray2 >= array2.length) {
arrayCopy(array1, indexOfArray1, destArr, i, array1.length - indexOfArray1);
int actualSize = i + array1.length - indexOfArray1;
return copyOf(destArr, actualSize);
}
if (array1[indexOfArray1] < array2[indexOfArray2]) {
destArr[i] = array1[indexOfArray1];
indexOfArray1++;
} else if (array1[indexOfArray1] == array2[indexOfArray2]) {
destArr[i] = array1[indexOfArray1];
indexOfArray1++;
indexOfArray2++; // 去除重复元素
} else {
destArr[i] = array2[indexOfArray2];
indexOfArray2++;
}
}
// array1.length、array2.length均为0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[] original, int newLength) {
int[] dest = new int[newLength];
for (int i = 0; i < newLength; i++) {
dest[i] = original[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 newSize = oldArray.length + size;
int[] newArray = new int[newSize];
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();
}
if (max == 1) {
return new int[] {};
}
ArrayList list = new ArrayList();
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;
}
i++;
}
return intListToArray(list);
}
private int[] intListToArray(List list) {
int[] array = new int[list.size()];
for (int i = 0; i < list.size(); i++) {
array[i] = (int) list.get(i);
}
return array;
}
/**
* 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 < 0) {
throw new IllegalArgumentException();
}
ArrayList list = new ArrayList();
for (int i = 2; i < max; i++) {
if (isPrime(i)) {
list.add(i);
}
}
return intListToArray(list);
}
private boolean isPrime(int num) {
for (int i = 2; i <= num / 2; i++) {
if (num % 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 list = new ArrayList();
for (int i = 2; i < max; i++) {
if (isPerfectNumber(i)) {
list.add(i);
}
}
return intListToArray(list);
}
private boolean isPerfectNumber(int num) {
int sumOfFactor = 1;
for (int i = 2; i <= num / 2; i++) {
if (num % i == 0) {
sumOfFactor += i;
}
}
if (sumOfFactor == num) {
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 s
* @return
*/
public String join(int[] array, String seperator) {
if (array == null) {
throw new IllegalArgumentException();
}
if (array.length == 0) {
return "";
}
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());
}
}