package com.coderising.array;
import java.util.ArrayList;
/**
* Created by yrs on 2017/3/3.
*/
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(null == origin || 0 == origin.length || 1 == origin.length) {
return;
}else {
for(int i=0; i < (origin.length/2); i++) {
int stmp = origin[i];
origin[i] = origin[origin.length-1-i];
origin[origin.length-1-i] = stmp;
}
}
}
/**
* 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){
if(null == oldArray || 0 == oldArray.length) {
return oldArray;
}
ArrayList stmp = new ArrayList();
for(int item: oldArray) {
if(item != 0)
stmp.add(item);
}
int[] newArray = arrayListToIntArray(stmp);
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){
ArrayList<Integer> arrayList = new ArrayList();
int i=0,j=0;
while (i<array1.length && j<array2.length) {
if(array1[i] < array2[j]) {
arrayList.add(array1[i++]);
}else {
if(array1[i] == array2[j])
i++;
arrayList.add(array2[j++]);
}
}
while (i<array1.length) {
arrayList.add(array1[i++]);
}
while (j<array2.length) {
System.out.println(j);
arrayList.add(array2[j++]);
}
int[] newArray = arrayListToIntArray(arrayList);
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){
if(size < 0) {
throw new IndexOutOfBoundsException();
}
if(null == oldArray || 0 == oldArray.length) {
int[] newArray = new int[size];
return newArray;
}
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){
if(max < 0) {
throw new IndexOutOfBoundsException("max value error, max = " + max);
}
if(1 == max) {
int[] fib = {};
return fib;
}
ArrayList<Integer> fibAL = new ArrayList();
int before = 1;
int next = 1;
int stmp;
fibAL.add(before);
fibAL.add(next);
while ((before + next) <max) {
fibAL.add(before+next);
stmp = before;
before = next;
next = next + stmp;
}
int[] fib = arrayListToIntArray(fibAL);
return fib;
}
/**
* 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 null;
}
ArrayList<Integer> arrayList = new ArrayList();
for (int i=2; i<max; i++) {
if (isPrime(i)){
arrayList.add(i);
}
}
int[] primes = arrayListToIntArray(arrayList);
return primes;
}
/**
* 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 < 6){
return null;
}
ArrayList<Integer> arrayList = new ArrayList();
for(int i=6; i<max; i++) {
if(isPerfect(i)){
arrayList.add(i);
}
}
int[] perfect = arrayListToIntArray(arrayList);
return perfect;
}
/**
* 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 seperator
* @return
*/
public String join(int[] array, String seperator){
if(null == array || 0 == array.length) {
return seperator;
}
String str = "";
for(int i=0; i<array.length-1; i++) {
str += (array[i] + seperator);
}
str += array[array.length-1];
return str;
}
private int[] arrayListToIntArray(ArrayList<Integer> arrayList) {
int[] array = new int[arrayList.size()];
for(int i=0; i<arrayList.size(); i++) {
array[i] = arrayList.get(i);
}
return array;
}
private boolean isPrime(int a) {
boolean result = true;
for(int i=2; i<=Math.sqrt(a); i++) {
if(a%i == 0) {
result = false;
break;
}
}
return result;
}
private boolean isPerfect(int a) {
ArrayList<Integer> arrayList = new ArrayList();
for(int i=1; i<=Math.sqrt(a); i++) {
if(a % i == 0) {
arrayList.add(i);
arrayList.add(a / i);
}
}
int sum = 0;
for(int item: arrayList) {
sum += item;
}
if(sum-a == a) {
return true;
}
return false;
}
}