package algorithm;
import datastructure.basic.ArrayList;
import java.util.stream.Stream;
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 head = 0;
int rear = origin.length - 1;
for (; head < rear; ++head, --rear) {
if (origin[head] != origin[rear]) {
int t = origin[head];
origin[head] = origin[rear];
origin[rear] = t;
}
}
}
/**
* 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 count = 0;
int[] tempArray = new int[oldArray.length];
for (int i : oldArray) {
if (i != 0) {
tempArray[count++] = i;
}
}
int[] newArray = new int[count];
System.arraycopy(tempArray, 0, newArray, 0, count);
return newArray;
}
/**
* 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) {
int[] tempArray = new int[array1.length + array2.length];
int count = 0;
int p1 = 0, p2 = 0;
while (p1 < array1.length && p2 < array2.length) {
if (array1[p1] < array2[p2]) {
if (count == 0 || array1[p1] != tempArray[count - 1]) {
tempArray[count++] = array1[p1];
}
p1++;
} else if (array1[p1] > array2[p2]) {
if (count == 0 || array2[p2] != tempArray[count - 1]) {
tempArray[count++] = array2[p2++];
}
p2++;
} else {
if (count == 0 || array1[p1] != tempArray[count - 1]) {
tempArray[count++] = array1[p1++];
}
p1++;
p2++;
}
}
while (p1 < array1.length) {
if (count == 0 || array1[p1] != tempArray[count - 1]) {
tempArray[count++] = array1[p1];
}
p1++;
}
while (p2 < array2.length) {
if (count == 0 || array2[p2] != tempArray[count - 1]) {
tempArray[count++] = array2[p2];
}
p2++;
}
int[] newArray = new int[count];
System.arraycopy(tempArray, 0, newArray, 0, count);
return newArray;
}
/**
* 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.size + 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) {
if (max <= 1) {
return new int[0];
}
ArrayList list = new ArrayList();
list.add(1);
list.add(1);
while (true) {
int a = (int) (list.get(list.size() - 1));
int b = (int) (list.get(list.size() - 2));
if (a + b < max) {
list.add(a + b);
} else {
break;
}
}
int[] result = new int[list.size()];
for (int i = 0; i < list.size(); ++i) {
result[i] = (int) list.get(i);
}
return result;
}
/**
* 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[0];
}
ArrayList list = new ArrayList();
for (int i = 2; true; ++i) {
if (i >= max) {
break;
} else if (isPrime(i)) {
list.add(i);
}
}
int[] result = new int[list.size()];
for (int i = 0; i < list.size(); ++i) {
result[i] = (int) list.get(i);
}
return result;
}
private boolean isPrime(int n) {
for (int i = 2; i <= Math.sqrt(n); ++i) {
if (n % 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 <= 6) {
return new int[0];
}
ArrayList list = new ArrayList();
for (int i = 2; true; ++i) {
if (i >= max) {
break;
} else if (isPerfect(i)) {
list.add(i);
}
}
int[] result = new int[list.size()];
for (int i = 0; i < list.size(); ++i) {
result[i] = (int) list.get(i);
}
return result;
}
private boolean isPerfect(int n) {
int sum = 1;
for (int i = 2; i <= n / 2; ++i) {
if (sum > n) {
return false;
}
if (n % i == 0) {
sum += i;
}
}
return sum == n;
}
/**
* 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) {
if (array.length == 0) {
return "";
}
StringBuilder builder = new StringBuilder();
builder.append(array[0]);
for (int i = 1; i < array.length; ++i) {
builder.append(seperator).append(array[i]);
}
return builder.toString();
}
}