package com.coderising.array;
import java.util.ArrayList;
import java.util.List;
/**
* ArrayUtil
*
* Created by Korben on 26/02/2017.
*/
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]
*/
public static void reverseArray(int[] origin) {
ensureNotNull(origin);
int length = origin.length;
for (int i = 0; i < length / 2; i++) {
int tmp = origin[i];
origin[i] = origin[length - i - 1];
origin[length - i - 1] = tmp;
}
}
/**
* 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}
*/
public static int[] removeZero(int[] oldArray) {
ensureNotNull(oldArray);
int nonZeroCount = 0;
for (int i : oldArray) {
if (i != 0) {
nonZeroCount++;
}
}
int newArr[] = new int[nonZeroCount];
int newArrIndex = 0;
for (int i : oldArray) {
if (i != 0) {
newArr[newArrIndex++] = i;
}
}
return newArr;
}
/**
* 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
*/
public static int[] merge(int[] array1, int[] array2) {
ensureNotNull(array1);
ensureNotNull(array2);
int maxArraySize = array1.length + array2.length;
int[] mergedArray = new int[maxArraySize];
int index1 = 0;
int index2 = 0;
int mergedIndex = -1;
for (int i = 0; i < maxArraySize; i++) {
if (index1 == array1.length) {
System.arraycopy(array2, index2, mergedArray, mergedIndex + 1, array2.length - index2);
mergedIndex += array2.length - index2;
break;
} else if (index2 == array2.length) {
System.arraycopy(array1, index1, mergedArray, mergedIndex + 1, array1.length - index1);
mergedIndex += array1.length - index1;
break;
} else {
int compare = Integer.compare(array1[index1], array2[index2]);
if (compare < 0) {
mergedArray[++mergedIndex] = array1[index1++];
} else if (compare > 0) {
mergedArray[++mergedIndex] = array2[index2++];
} else {
mergedArray[++mergedIndex] = array1[index1++];
index2++;
}
}
}
// 清除数组多余部分
if (mergedIndex + 1 < maxArraySize) {
int[] resultArray = new int[mergedIndex + 1];
System.arraycopy(mergedArray, 0, resultArray, 0, mergedIndex + 1);
return resultArray;
}
return mergedArray;
}
/**
* 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]
*/
public static int[] grow(int[] oldArray, int size) {
ensureNotNull(oldArray);
if (size < 0) {
throw new IllegalArgumentException("size must > 0");
}
int[] newArray = new int[oldArray.length + size];
System.arraycopy(oldArray, 0, newArray, 0, oldArray.length);
for (int i = oldArray.length; i < newArray.length; i++) {
newArray[i] = 0;
}
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 []
*/
public static int[] fibonacci(int max) {
if (max == 1) {
int[] array = new int[1];
array[1] = 1;
return array;
}
List<Integer> list = new ArrayList<>();
for (int i = 1; ; i++) {
int fibonacciNumber = getFibonacciNumber(i);
if (fibonacciNumber <= max) {
list.add(fibonacciNumber);
} else {
break;
}
}
return list2Array(list);
}
private static int getFibonacciNumber(int index) {
if (index == 1) {
return 1;
}
if (index == 2) {
return 1;
}
return getFibonacciNumber(index - 2) + getFibonacciNumber(index - 1);
}
/**
* 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]
*/
public static int[] getPrimes(int max) {
List<Integer> primeList = new ArrayList<>();
if (max <= 1) {
return new int[0];
}
if (max >= 2) {
primeList.add(2);
}
// 所有偶数都不是素数, 所以这里采用 i += 2
for (int i = 3; i < max; i += 2) {
if (isPrimeNumber(i, primeList)) {
primeList.add(i);
}
}
return list2Array(primeList);
}
private static boolean isPrimeNumber(int number, List<Integer> primeList) {
for (Integer prime : primeList) {
if (number % prime == 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
*/
public static int[] getPerfectNumbers(int max) {
if (max <= 1) {
return new int[0];
}
List<Integer> perfectNumberList = new ArrayList<>();
for (int i = 2; i < max; i++) {
if (isPerfectNumber(i)) {
perfectNumberList.add(i);
}
}
return list2Array(perfectNumberList);
}
private static boolean isPerfectNumber(int number) {
int sum = 1;
for (int i = 2; i <= number / 2; i++) {
if (number % i == 0) {
sum += i;
}
}
return sum == number;
}
/**
* 用separator 把数组 array给连接起来
* 例如array= [3,8,9], separator = "-"
* 则返回值为"3-8-9"
*/
public static String join(int[] array, String separator) {
ensureNotNull(array);
if (separator == null) {
throw new NullPointerException();
}
StringBuilder stringBuilder = new StringBuilder();
for (int i = 0; i < array.length; i++) {
stringBuilder.append(array[i]);
if (i != array.length - 1) {
stringBuilder.append(separator);
}
}
return stringBuilder.toString();
}
private static int[] list2Array(List<Integer> list) {
int[] result = new int[list.size()];
for (int i = 0; i < list.size(); i++) {
result[i] = list.get(i);
}
return result;
}
private static void ensureNotNull(int[] array) {
if (array == null) {
throw new NullPointerException();
}
}
}