package xdx.homework.second.array;
import xdx.homework.first.ArrayList;
import xdx.homework.first.List;
import xdx.homework.first.Queue;
import xdx.homework.first.Stack;
import java.util.Arrays;
import static java.lang.StrictMath.sqrt;
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) {
int end = origin.length - 1;
for (int begin = 0; begin < end; begin++, end--) {
// 交换首尾
origin[begin] = origin[begin] ^ origin[end];
origin[end] = origin[begin] ^ origin[end];
origin[begin] = origin[begin] ^ origin[end];
}
}
/**
* 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[] newArray = new int[oldArray.length];
int newArrayIndex = 0;
int i = 0;
for (; i < oldArray.length; i++) {
if (oldArray[i] == 0) continue;
newArray[newArrayIndex++] = oldArray[i];
}
return Arrays.copyOfRange(newArray, 0, newArrayIndex);
}
/**
* 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) {
// 分别放进两个栈中,取小的出栈
Queue<Integer> queue1 = new Queue<>();
Queue<Integer> queue2 = new Queue<>();
ArrayList<Integer> newArray = new ArrayList<>();
for (int a : array1) {
queue1.enQueue(a);
}
for (int a : array2) {
queue2.enQueue(a);
}
while (!queue1.isEmpty() && !queue2.isEmpty()) {
if (queue1.getFront() < queue2.getFront()) {
newArray.add(queue1.deQueue());
} else if (queue1.getFront() > queue2.getFront()) {
newArray.add(queue2.deQueue());
} else {
newArray.add(queue2.deQueue());
queue1.deQueue();
}
}
while (!queue1.isEmpty()) newArray.add(queue1.deQueue());
while (!queue2.isEmpty()) newArray.add(queue2.deQueue());
int[] retArray = new int[newArray.size()];
for (int i = 0; i < newArray.size(); i++) {
retArray[i] = newArray.get(i);
}
return retArray;
}
/**
* 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) {
int[] newArray = new int[oldArray.length + size];
System.arraycopy(oldArray, 0, newArray, 0, oldArray.length);
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) {
int first = 1;
int second = 1;
if (max == 0) return new int[]{0};
if (max == 1) return new int[]{first, second};
List<Integer> fibList = new ArrayList<>();
fibList.add(first);
fibList.add(second);
int last = first + second;
while (last < max) {
fibList.add(last);
first = second;
second = last;
last = first + second;
}
return list2array(fibList);
}
/**
* 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 new int[]{};
if (max == 2) return new int[]{2};
List<Integer> primeList = new ArrayList<>();
primeList.add(2);
for (int i = 3; i <= max; i += 2) {
// 判断i是不是素数
boolean isPrime = true;
for (int j = 2; j <= Math.sqrt(i); j++) {
if (i % j == 0) isPrime = false;
}
if (isPrime) primeList.add(i);
}
return list2array(primeList);
}
/**
* 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 < 1) return new int[]{};
List<Integer> perfectNums = new ArrayList<>();
for (int aPerfectNum = 1; aPerfectNum <= max; aPerfectNum++) {
int sumFactors = 1;
for (int factor = 2; factor <= aPerfectNum / 2; factor++) {
if (aPerfectNum % factor == 0) {
sumFactors += factor;
}
}
if (sumFactors == aPerfectNum) perfectNums.add(aPerfectNum);
}
return list2array(perfectNums);
}
/**
* 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 seperator
* @return
*/
public String join(int[] array, String seperator) {
StringBuilder stringBuilder = new StringBuilder();
for (int a : array) {
stringBuilder.append(a).append(seperator);
}
stringBuilder.deleteCharAt(stringBuilder.length() - 1);
return stringBuilder.toString();
}
private int[] list2array(List<Integer> list) {
int[] array = new int[list.size()];
for (int i = 0; i < list.size(); i++) {
array[i] = list.get(i);
}
return array;
}
}