package com.coderising.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 void reverseArray(int[] origin){
int i, tmp;
int len = origin.length;
for (i = 0; i < len/2; i++) {
tmp = origin[i];
origin[i] = origin[len - i - 1];
origin[len - i - 1] = tmp;
}
}
/**
* 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 newLen = 0;
int[] tmpArray = new int[oldArray.length];
for (int item:oldArray) {
if (item != 0) {
tmpArray[newLen++] = item;
}
}
int[] newArray = new int[newLen];
System.arraycopy(tmpArray, 0, newArray, 0, newLen);
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 i = 0, j = 0, newLen = 0;
int len1 = array1.length, len2 = array2.length;
int[] tmpArray = new int[len1+len2];
while (i < len1 && j < len2) {
if (array1[i] < array2[j]) {
tmpArray[newLen++] = array1[i++];
}
else if (array1[i] > array2[j]) {
tmpArray[newLen++] = array2[j++];
}
else {
tmpArray[newLen++] = array1[i];
i++;
j++;
}
}
if (i < len1) {
System.arraycopy(array1, i, tmpArray, newLen, len1 - i);
newLen += (len1 - i);
}
else if (j < len2) {
System.arraycopy(array2, j, tmpArray, newLen, len2 - j);
newLen += (len2 - j);
}
int[] newArray = new int[newLen];
System.arraycopy(tmpArray, 0, newArray, 0, newLen);
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){
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 realSize = 0;
int[] array = new int[10];
int[] resultArray;
int x0 = 1, x1 = 1;
int tmp;
if (max <= x0) {
return new int[0];
}
for (array[realSize++] = x0; max > x1; tmp = x0 + x1, x0 = x1, x1 = tmp) {
if (realSize + 1 > array.length) {
array = grow(array, 5);
}
array[realSize++] = x1;
}
if (array.length > realSize) {
resultArray = new int[realSize];
System.arraycopy(array, 0, resultArray, 0, realSize);
}
else {
resultArray = array;
}
return resultArray;
}
/**
* 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
*/
private boolean isPrime(int num) {
for (int i = 2; i <= num/2; i++) {
if (num % i == 0) {
return false;
}
}
return true;
}
public int[] getPrimes(int max){
int realSize = 0;
int[] array = new int[10];
int[] resultArray;
for (int num = 2; num < max; num++) {
if (isPrime(num)) {
if (realSize + 1 > array.length) {
array = grow(array, 5);
}
array[realSize++] = num;
}
}
if (array.length > realSize) {
resultArray = new int[realSize];
System.arraycopy(array, 0, resultArray, 0, realSize);
}
else {
resultArray = array;
}
return resultArray;
}
/**
* 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
*/
private int exponentiation(int base, int expo) {
int result = 1;
for (int i = 0; i < expo; i++) {
result *= base;
}
return result;
}
/*
* a perfect number = 2^(n-1) * (2^n - 1), where (2^n - 1) is a prime
*/
public int[] getPerfectNumbers(int max){
int realSize = 0;
int[] array = new int[10];
int[] resultArray;
int num = 0;
int x1, x2;
for (int i = 2; true; i++) {
x2 = exponentiation(2, i) - 1;
if (x2 >= max) {
break;
}
if (!isPrime(x2)) {
continue;
}
x1 = exponentiation(2, i - 1);
num = x1 * x2;
if (num >= max) {
break;
}
if (realSize + 1 > array.length) {
array = grow(array, 5);
}
array[realSize++] = num;
}
if (array.length > realSize) {
resultArray = new int[realSize];
System.arraycopy(array, 0, resultArray, 0, realSize);
}
else {
resultArray = array;
}
return resultArray;
}
/**
* 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 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);
}
if (array.length > 0)
sb.append(array[array.length-1]);
return sb.toString();
}
}