package com.coding.basic.array;
import java.util.Arrays;
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 || origin.length == 0){
return;
}
int temp ;
for (int i = 0; i < (origin.length / 2); i++) {
temp = origin[i];
origin[i] = origin[(origin.length - 1) - i];
origin[(origin.length - 1)- i] = 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 static int[] removeZero(int[] oldArray){
if (oldArray == null ){
return null;
}
if (oldArray.length == 0){
return oldArray;
}
int count = 0;
int[] temp = new int[oldArray.length];
for (int i = 0; i < oldArray.length; i++) {
if (oldArray[i] != 0){
temp[count++] = oldArray[i];
}
}
int[] result = new int[count];
System.arraycopy(temp, 0, result, 0, count);
return result;
}
/**
* 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 null;
}
if (array1 == null){
return array2;
}
if (array2 == null){
return array1;
}
int length1 = array1.length;
int length2 = array2.length;
int[] temp = new int[length1 + length2];
int i,j,k;
for ( i = 0, j = 0, k = 0; i < length1 && j < length2 ;) {
if (array1[i] < array2[j]){
temp[k++] = array1[i++];
}else if (array1[i] > array2[j]){
temp[k++] = array2[j++];
}else {
temp[k++] = array1[i];
i++;
j++;
}
}
while (i < length1){
temp[k++] = array1[i++];
}
while (j < length2){
temp[k++] = array2[j++];
}
int[] result = new int[k];
System.arraycopy(temp, 0, result, 0, k);
return result;
}
/**
* 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){
int oldSize = oldArray.length;
int[] newArray = new int[oldSize + size];
System.arraycopy(oldArray, 0, newArray, 0, oldSize);
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[] fibonacci1(int max){
if (max == 1){
return new int[0];
}
int[] temp = new int[max];
int count = 0;
// for (int i = 1; i < max; i++) {
// int num = fibonacci(i);
// if (num < max){
// temp[count++] = num;
// }else {
// break;
// }
// }
temp[0] = 1;
temp[1] = 2;
for (int i = 2; i < max; i++) {
temp[i] = temp[i-1] + temp[i-2]; //直接在数组中实现斐波那契数列
if (temp[i] >= max){
break;
}else {
count++;
}
}
return Arrays.copyOf(temp, count);
}
private static int fibonacci(int n){
if (n <= 0){
throw new IllegalArgumentException();
}
if (n == 1 || n == 2) {
return 1;
}
return fibonacci(n - 1) + fibonacci(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 <= 2){
return new int[0];
}
int[] temp = new int[max];
int count = 0;
for (int i = 2; i < max; i++) {
int j;
for ( j = 2; j * j < i; j++) {
if (i % j == 0){
break;
}
}
if (j * j >= i){
temp[count++] = i;
}
}
return Arrays.copyOf(temp, count);
}
/**
* 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 <= 1){
return new int[0];
}
ArrayList<Integer> array = new ArrayList<>();
for (int i = 2; i < max; i++) {
int sum = 0; //存储因子和
for (int j = 1; j < i; j++) {
if (i % j == 0){
sum += j;
}
}
if (sum == i){
array.add(i);
}
}
int[] result = new int[array.size()];
for (int i = 0; i < array.size(); i++) {
result[i] = array.get(i);
}
return result;
}
/**
* 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 || array.length == 0){
return null;
}
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();
}
}