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){
if (origin != null && origin.length > 1) {
int len = origin.length;
int temp;
for(int left = 0,right = len - 1; left < right; left++,right = len - left - 1){
temp = origin[left];
origin[left] = origin[right];
origin[right] = temp;
}
}
}
/**
* 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[] newArray = null;
if (oldArray != null && oldArray.length > 0) {
int[] indexArray = new int[oldArray.length];
int j = 0;
for (int i = 0; i < oldArray.length; i++) {
if(oldArray[i] != 0){
indexArray[j++] = i;
}
}
newArray = new int[j];
for (int i = 0; i < j; i++) {
newArray[i] = oldArray[indexArray[i]];
}
indexArray = null;
}
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 == null || array1.length <= 0){
return array2;
}
if(array2 == null || array2.length <= 0){
return array1;
}
int[] tempArray = new int[array1.length + array2.length];
int i = 0,j = 0,k = 0;
for (; i < array1.length && j < array2.length; ) {
if (array1[i] > array2[j]) {
tempArray[k++] = array2[j++];
}
else if(array1[i] < array2[j]){
tempArray[k++] = array1[i++];
}
else {
tempArray[k++] = array1[i++];
j++;
}
}
// 以array1为结束点
if(array1[array1.length - 1] > array2[array2.length - 1]){
for (; i < array1.length;) {
tempArray[k++] = array1[i++];
}
} else { // 以array2为结束点
for (; j < array2.length;) {
tempArray[k++] = array1[j++];
}
}
int[] mergeArray = new int[k];
for (int l = 0; l < mergeArray.length; l++) {
mergeArray[l] = tempArray[l];
}
tempArray = null;
return mergeArray;
}
/**
* 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(size <= 0){
throw new RuntimeException("size大于0");
}
int[] newArray = null;
if(oldArray != null && oldArray.length > 0){
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 int[] fibonacci(int max){
if(max <= 1){
return new int[0];
}
int[] tempArray = new int[max];
int i = 0;
tempArray[i++] = 1;
tempArray[i] = 1;
while(tempArray[i] < max){
i++;
tempArray[i] = tempArray[i - 1] + tempArray[i - 2];
}
int[] array = new int[i];
for (int j = 0; j < array.length; j++) {
array[j] = tempArray[j];
}
tempArray = null;
return array;
}
/**
* 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];
}
int[] tempArray = new int[max];
int j = 0;
for (int i = 2; i < max; i++) {
if(isPrime(i)){
tempArray[j++] = i;
}
}
int[] array = new int[j];
for (int i = 0; i < j; i++) {
array[i] = tempArray[i];
}
tempArray = null;
return array;
}
private boolean isPrime(int i) {
for (int j = 2; j < i; j++) {
if(i % j == 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 <= 2){
return new int[0];
}
int[] tempArray = new int[max];
int j = 0;
for (int i = 3; i < max; i++) {
if(isPerfectNumber(i)){
tempArray[j++] = i;
}
}
int[] array = new int[j];
for (int i = 0; i < j; i++) {
array[i] = tempArray[i];
}
tempArray = null;
return array;
}
private boolean isPerfectNumber(int num) {
int sum = 1;
for(int i = 2; i < num; i++){
if(num % i == 0){
sum += i;
}
}
if(sum == num){
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 String join(int[] array, String seperator){
char[] chars = new char[array.length<<1];
for (int i = 0,j = 1; i < chars.length; i+=2,j+=2) {
chars[i] = (char) (array[i>>1] + 48);
chars[j] = seperator.charAt(0);
}
return new String(chars, 0, chars.length - 1);
}
}