package com.sprint.array;
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 static void reverseArray(int[] origin){
if (origin == null) {
return;
}
int length = origin.length;
int[] temp = new int[length];
for (int i = 0; i < length; i++)
temp[i] = origin[i];
for (int i = length - 1, j = 0; i >= 0 && j < length; i--, j++)
origin[j] = temp[i];
}
/**
* 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 static int[] removeZero(int[] oldArray){
if (oldArray == null) {
return new int[0];
}
int zeroCount = 0;
for (int i = 0; i < oldArray.length; i++) {
if (oldArray[i] == 0)
zeroCount++;
}
int[] newArray = new int[oldArray.length-zeroCount];
for (int i = 0, j = 0; i < oldArray.length && j < newArray.length; i++) {
if (oldArray[i] != 0) {
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 static int[] merge(int[] array1, int[] array2){
if (array1 == null && array2 == null)
return new int[0];
int index1 = 0, index2 = 0;
int[] array3 = new int[array1.length + array2.length];
int index = 0;
while (index1 != array1.length && index2 != array2.length) {
if (array1[index1] < array2[index2]) {
array3[index++] = array1[index1++];
} else if (array1[index1] > array2[index2]) {
array3[index++] = array2[index2++];
} else if (array1[index1] == array2[index2]){
array3[index++] = array1[index1++];
index2++;
}
}
if (index1 == array1.length && index2 != array2.length) {
for (int i = index2; i < array2.length; i++)
array3[index++] = array2[i];
} else if (index2 == array2.length && index1 != array1.length) {
for (int i = index1; i < array1.length; i++) {
array3[index++] = array1[i];
}
}
int[] newArray = new int[index];
for (int i = 0; i < newArray.length; i++)
newArray[i] = array3[i];
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 static int[] grow(int [] oldArray, int size){
if (size <= 0)
return new int[0];
int[] newArray = new int[oldArray.length + size];
for (int i = 0; i < oldArray.length; i++) {
newArray[i] = oldArray[i];
}
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 static int[] fibonacci(int max){
if (max < 1)
return new int[0];
if (max == 1)
return new int[0];
int[] array = new int[max];
int i = 0;
int value = fibonaccis(i+1);
while ( value < max) {
array[i++] = value;
value = fibonaccis(i+1);
}
int[] newArray = new int[i];
for (int j = 0; j < newArray.length; j++) {
newArray[j] = array[j];
}
return newArray;
}
private static int fibonaccis(int n) {
if (n <=0)
return 0;
if (n == 1 || n ==2 )
return 1;
return fibonaccis(n-1)+fibonaccis(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 static int[] getPrimes(int max){
if (max <= 1) {
return new int[0];
}
int[] array = new int[max];
int index = 0;
for (int i = 2; i < max; i++) {
if (i == 2 || i == 3 || i == 5 || i == 7)
array[index++] = i;
if (i%2 !=0 && i%3 != 0 && i%5 != 0 && i%7 != 0)
array[index++] = i;
}
int[] newArray = new int[index];
for (int i = 0; i < newArray.length; i++) {
newArray[i] = array[i];
}
return newArray;
}
/**
* 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 static int[] getPerfectNumbers(int max){
if (max <= 0)
return new int[0];
int[] array = new int[max];
int index = 0;
for (int i = 1; i < max; i++) {
if (isPerfectNumber(i))
array[index++] = i;
}
int[] newArray = new int[index];
for (int i = 0; i < newArray.length; i++)
newArray[i] = array[i];
return newArray;
}
private static boolean isPerfectNumber(int n) {
int sum = 0;
int i = 1;
while (i < n) {
if (n%i == 0)
sum += i;
i++;
}
if (sum == n)
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 s
* @return
*/
public static String join(int[] array, String seperator){
if (array == null)
return null;
StringBuilder str = new StringBuilder();
for (int i = 0; i < array.length; i++) {
if (i == array.length-1)
str.append(array[i]);
else
str.append(array[i] + seperator);
}
return str.toString();
}
}