package com.coding.week2.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 void reverseArray(int[] origin){
int[] newArr = new int[origin.length];
for(int i = origin.length - 1,j = 0; i >= 0; i--,j++){
newArr[j] = origin[i];
}
System.arraycopy(newArr, 0, origin, 0, origin.length);
}
/**
* 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[] newArr = new int[oldArray.length];
int j = 0;
for(int i = 0; i < oldArray.length; i++){
if(oldArray[i] != 0)
newArr[j++] = oldArray[i];
}
int[] newArr1 = new int[j];
System.arraycopy(newArr, 0, newArr1, 0, j);
return newArr1;
}
/**
* 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 len = array1.length > array2.length ? array1.length : array2.length;
int[] newArr = new int[len];
for(int i = 0; i < array1.length; i++){
for(int j : array2){
if(array1[i] == j){
newArr[i] = array1[i];
}
}
}
int[] newArr2 = new int[array1.length - newArr.length];
for(int i = 0; i < array1.length; i++){
for(int j : newArr){
if(array1[i] == j)
continue;
}
}
int[] newArr1 = new int[array1.length + array2.length];
System.arraycopy(array2, 0, newArr1, 0, array2.length);
System.arraycopy(newArr, 0, newArr1, array2.length-1, newArr.length);
bubuleSort(newArr1);
return newArr1;
}
public void bubuleSort(int[] newArr1){
for(int i = 0; i < newArr1.length; i++){
for(int j = 0; j < newArr1.length; j++)
if(newArr1[i] < newArr1[j]){
int temp = newArr1[i];
newArr1[i] = newArr1[j] ;
newArr1[j] = temp;
}
}
}
/**
* 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[] newArr = new int[oldArray.length + size];
for(int i = 0; i < newArr.length; i++){
if (i < oldArray.length){
newArr[i] = oldArray[i];
}else
newArr[i] = 0;
}
return newArr;
}
/**
* 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){
//1 得到小于max的斐波那契数
//2
if( max == 1)
return new int[]{};
int[] arr = new int[3];
arr[0] = 1;
arr[1] = 1;
arr[2] = arr[0] + arr[1];
if(max == 2)
return arr;
int i = 2;
while (max > arr[i]){
if(i+1 >= arr.length){
int capacity = arr.length + (arr.length >> 1);
int[] newArr = new int[capacity];
System.arraycopy(arr, 0, newArr, 0, arr.length);
arr = newArr;
}
arr[++i] = arr[i - 1] + arr[i - 2];
if(arr[i] < 0){
System.out.println(Arrays.toString(arr));
throw new OutOfMemoryError();
}
}
return removeZero(arr);
}
/**
* 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[]{};
int[] arr = new int[max];
for(int i = max; i >= 2; i--){
if(isPrime(i)){
arr[i] = i;
}
}
return removeZero(arr);
}
private boolean isPrime(int value){
for(int i = 2; i < Math.sqrt(value); i++){
if(value % 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[] ints = new int[max+1];
for(int i = 1; i <= max; i++){
if(isPerfectNum(i)){
ints[i] = i;
}
}
return removeZero(ints);
}
private boolean isPerfectNum(int value){
if(value == 1)
return false;
int sum = 0;
for(int i = 1; i <= Math.sqrt(value); i++){
if(value % i == 0){
sum += i + value / i;
}
}
return sum-value == value;
}
/**
* 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
* @return
*/
public String join(int[] array, String seperator){
StringBuilder builder = new StringBuilder();
for(int i = 0; i < array.length; i++){
builder.append(array[i]);
if(i != array.length - 1)
builder.append(seperator);
}
return builder.toString();
}
}