package com.aaront.exercise;
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 (origin == null || origin.length == 0) return;
int head = 0;
int tail = origin.length - 1;
while (head < tail) {
origin[head] = origin[head] ^ origin[tail];
origin[tail] = origin[head] ^ origin[tail];
origin[head] = origin[head] ^ origin[tail];
head++;
tail--;
}
}
/**
* 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) return new int[0];
int size = oldArray.length;
for (int i = 0; i < size; i++) {
if (oldArray[i] != 0) continue;
int j = i + 1;
for (; j < size; j++) {
if (oldArray[j] != 0) break;
}
size -= (j - i);
move(oldArray, i, j - i, size);
}
int[] newArray = new int[size];
for (int i = 0; i < size; i++) {
newArray[i] = oldArray[i];
}
return newArray;
}
private void move(int[] array, int start, int moveLen, int size) {
for (int i = start; i < size; i++) {
array[i] = array[i + moveLen];
}
}
/**
* 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 len1 = array1.length;
int len2 = array2.length;
int[] mergeArray = new int[len1 + len2];
int i = 0;
int j = 0;
int k = 0;
for (; i < len1 && j < len2; ) {
if (array1[i] < array2[j]) {
mergeArray[k] = array1[i];
i++;
} else if (array1[i] > array2[j]) {
mergeArray[k] = array2[j];
j++;
} else {
mergeArray[k] = array1[i];
i++;
j++;
}
k++;
}
while (i < len1) {
mergeArray[k++] = array1[i++];
}
while (j < len2) {
mergeArray[k++] = array2[j++];
}
return resize(mergeArray, k);
}
/**
* 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[0];
int[] newArray = new int[oldArray.length + size];
int index = 0;
for (int len = oldArray.length; index < len; index++) {
newArray[index] = oldArray[index];
}
for (int len = newArray.length; index < len; index++) {
newArray[index] = 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 []
*
* @param max
* @return
*/
public int[] fibonacci(int max) {
if (max <= 1) return new int[0];
int[] elements = new int[10];
elements[0] = 1;
elements[1] = 1;
int index = 1;
int sum;
while ((sum = elements[index] + elements[index - 1]) < max) {
if (index + 1 >= elements.length) elements = dilatation(elements);
elements[++index] = sum;
}
if (index < elements.length - 1) {
elements = resize(elements, index + 1);
}
return elements;
}
private int[] dilatation(int[] origin) {
int len = origin.length;
int[] newArray = new int[len * 2];
for (int i = 0; i < len; i++) {
newArray[i] = origin[i];
}
return newArray;
}
private int[] resize(int[] origin, int size) {
int[] newArray = new int[size];
for (int i = 0; i < size; i++) {
newArray[i] = origin[i];
}
return newArray;
}
/**
* 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) {
int[] primes = new int[max];
int index = 0;
for (int i = 2; i < max; i++) {
if (isPrimes(i)) {
primes[index++] = i;
}
}
return resize(primes, index);
}
private boolean isPrimes(int num) {
for (int i = 2; i < num; i++) {
if (num % 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[] perfectNumbers = new int[max];
int index = 0;
for (int i = 1; i < max; i++) {
int[] factors = getFactors(i);
int sum = 0;
for (int factor : factors) {
sum += factor;
}
if (sum == i) perfectNumbers[index++] = i;
}
return resize(perfectNumbers, index);
}
private int[] getFactors(int num) {
int[] factors = new int[num];
int index = 0;
for (int i = 1; i < num; i++) {
if (num % i == 0) {
factors[index++] = i;
}
}
return resize(factors, index);
}
/**
* 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 == null) return "";
StringBuilder sb = new StringBuilder("");
for(int i = 0, len = array.length;i<len;i++) {
sb.append(array[i]);
if(i != len - 1) sb.append(seperator);
}
return sb.toString();
}
}