package com.coderising.array;
import java.util.ArrayList;
import java.util.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 int[] reverseArray(int[] origin) {
if (origin == null || 0 == origin.length) {
throw new NullPointerException();
}
int N = origin.length;
for (int i = 0; i < N / 2; i++) {
int temp = origin[i];
origin[i] = origin[N - 1 - i];
origin[N - 1 - i] = temp;
}
return origin;
}
/**
* 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 || 0 == oldArray.length) {
throw new NullPointerException();
}
int count = 0;
for (int i = 0; i < oldArray.length; i++) {
if (0 != oldArray[i]) {
count++;
}
}
int[] newArray = new int[count];
int j = 0;
for (int i = 0; i < oldArray.length; i++) {
if (0 != oldArray[i]) {
newArray[j] = oldArray[i];
j++;
}
}
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) {
if (array1.length == 0 && array2.length == 0) {
throw new NullPointerException();
} else if (array1.length == 0) {
return array2;
} else if (array2.length == 0) {
return array1;
}
int count = array1.length + array2.length;
for (int i = 0; i < array1.length; i++) {
for (int j = 0; j < array2.length; j++) {
if (array1[i] == array2[j]) {
count--;
}
}
}
int[] newArray = new int[count];
int m = 0, n = 0;
for (int i = 0; i < count; i++) {
if (m == array1.length) {
System.arraycopy(array2, n, newArray, i, array2.length - n);
break;
}
if (n == array2.length) {
System.arraycopy(array1, m, newArray, i, array1.length - m);
break;
}
if (array1[m] < array2[n]) {
newArray[i] = array1[m];
m++;
} else if (array1[m] == array2[n]) {
newArray[i] = array1[m];
m++;
n++;
} else {
newArray[i] = array2[n];
n++;
}
}
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.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 || 0 == oldArray.length) {
int[] array = new int[size];
return array;
}
int[] target = new int[oldArray.length + size];
System.arraycopy(oldArray, 0, target, 0, oldArray.length);
return target;
}
/**
* 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 (0 == max) {
throw new IllegalArgumentException();
} else if (1 == max) {
int[] array = {};
return array;
}
int length = 0;
List<Integer> list = new ArrayList<>();
for (int i = 1; i < max; i++) {
if (fibo(i) < max) {
length++;
list.add(fibo(i));
} else {
break;
}
}
int[] array = new int[length];
for (int i = 0; i < length; i++) {
array[i] = list.get(i);
}
return array;
}
public int fibo(int N) {
if (N <= 2) {
return 1;
} else {
return fibo(N - 1) + fibo(N - 2);
}
}
/**
* 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) {
List<Integer> list = new ArrayList<>();
int count = 0;
for (int i = 0; i < max; i++) {
if (isPrime(i)) {
count++;
list.add(i);
}
}
int[] array = new int[count];
for (int i = 0; i < count; i++) {
array[i] = list.get(i);
}
return array;
}
public boolean isPrime(int N) {
if (N < 2) {
return false;
}
for (int i = 2; i * i <= 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) {
int count = 0;
List<Integer> list = new ArrayList<>();
for (int i = 1; i < max; i++) {
if (isPerfectNumber(i)) {
count++;
list.add(i);
}
}
int[] array = new int[count];
for (int i = 0; i < count; i++) {
array[i] = list.get(i);
}
return array;
}
public boolean isPerfectNumber(int N) {
int sum = 0;
for (int i = 1; i < N; i++) {
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) {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < array.length - 1; i++) {
sb.append(array[i]).append(seperator);
}
sb.append(array[array.length - 1]);
return sb.toString();
}
}