package com.coderising.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 (null == origin) {
return;
}
int first = 0;
int last = origin.length - 1;
int temp;
while (first < last) {
temp = origin[first];
origin[first] = origin[last];
origin[last] = temp;
first++;
last++;
}
}
/**
* 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[] resultArr = null;
if (null == oldArray) {
return resultArr;
}
int zeroSize = 0;
for (int i = 0; i < oldArray.length; i++) {
if (oldArray[i] == 0) {
zeroSize++;
}
}
resultArr = new int[oldArray.length - zeroSize];
int resultIndex = 0;
for (int i = 0; i < oldArray.length; i++) {
if (oldArray[i] != 0) {
resultArr[resultIndex] = oldArray[i];
resultIndex++;
}
}
return resultArr;
}
/**
* 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 (null == array1) {
return array2;
}
if (null == array2) {
return array1;
}
int[] resultArr = new int[array1.length + array2.length];
int index1 = 0;
int index2 = 0;
for (int i = 0; i < resultArr.length; i++) {
if (array1[index1] < array2[index2]) {
resultArr[i] = array1[index1];
index1++;
} else {
resultArr[i] = array2[index2];
index2++;
}
}
return resultArr;
}
/**
* 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 new int[size];
}
int[] resultArr = new int[oldArray.length + size];
for (int i = 0; i < oldArray.length; i++) {
resultArr[i] = oldArray[i];
}
return resultArr;
}
/**
* 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) {
ArrayList<Integer> tempList = new ArrayList<>();
int resultSize = 0;
while (fibonacci(tempList, resultSize) < max) {
resultSize++;
}
int[] resultArr = new int[resultSize];
for (int i = 0; i < resultSize; i++) {
resultArr[i] = tempList.get(i);
}
return resultArr;
}
/**
* 返回第index个斐波那契数列,resultArr用来存已经计算过的结果
*
* @param resultArr
* @param index
* @return
*/
private int fibonacci(ArrayList<Integer> resultArr, int index) {
if (resultArr.size() > index) {
return resultArr.get(index);
}
int newResult;
if (index == 0) {
newResult = 1;
} else if (index == 1) {
newResult = 1;
} else {
newResult = (resultArr.get(index - 1) == 0 ? resultArr.get(index - 1) : fibonacci(resultArr, index - 1))
+ (resultArr.get(index - 2) == 0 ? resultArr.get(index - 2) : fibonacci(resultArr, index - 2));
}
resultArr.add(newResult);
return newResult;
}
/**
* 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) {
return null;
}
ArrayList<Integer> tempList = new ArrayList<>();
for (int i = 2; i <= max; i++) {
if (isPrimes(tempList, i)) {
tempList.add(i);
}
}
int[] resultArr = new int[tempList.size()];
for (int i = 0; i < tempList.size(); i++) {
resultArr[i] = tempList.get(i);
}
return resultArr;
}
private boolean isPrimes(ArrayList<Integer> primesList, int temp) {
if (temp == 2 || temp == 3) {
return true;
}
for (int i = 0; i < primesList.size(); i++) {
if (temp % primesList.get(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) {
return null;
}
ArrayList<Integer> tempList = new ArrayList<>();
for (int i = 2; i <= max; i++) {
if (isPerfectNumber(i)) {
tempList.add(i);
}
}
int[] resultArr = new int[tempList.size()];
for (int i = 0; i < tempList.size(); i++) {
resultArr[i] = tempList.get(i);
}
return resultArr;
}
private boolean isPerfectNumber(int temp) {
if (temp == 1) {
return true;
}
int sum = 0;
for (int i = 1; i < temp; i++) {
if (temp % 1 == 0) {
if ((sum = sum + i) > temp) {
return false;
}
}
}
if (sum == temp) {
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 separator
* @return
*/
public String join(int[] array, String separator) {
if (null == array || array.length == 0 || null == separator) {
return null;
}
StringBuilder sb = new StringBuilder(array.length * (1 + separator.length()));
int i = 1;
sb.append(array[0]);
for (; i < array.length; i++) {
sb.append(separator);
sb.append(array[i]);
}
return sb.toString();
}
}