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==0){
throw new RuntimeException("invalid array argument!");
}
if(origin.length>1){
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 int[] removeZero(int[] oldArray){
if(oldArray==null || oldArray.length==0){
return oldArray;
}else{
int[] tmp = new int[oldArray.length];
int pos = 0;
for(int i=0;i<oldArray.length;i++){
if(oldArray[i]!=0){
tmp[pos]=oldArray[i];
pos++;
}
}
int[] result = new int[pos];
System.arraycopy(tmp, 0, result, 0, pos);
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 int[] merge(int[] array1, int[] array2){
//Check array sorting
checkIfArraySortedAsc(array1);
checkIfArraySortedAsc(array2);
//both are null then return null
if(array1==null && array2==null){
return null;
}
//one of them is empty array then return another
//Scenario:array1 is empty
if(array1.length==0){
if(array2 == null){
return array1;
}else{
return array2;
}
}else{
//Scenario:array1 is not empty
if(array2.length==0){
return array1;
//Scenario: both array1 and array2 are not empty
}else{
//Do merge in this case
int[] array3 = new int[array1.length+array2.length];
int pos1=0;
int pos2=0;
int pos3=0;
while(pos1<array1.length || pos2<array2.length){
if(pos1==array1.length){
array3[pos3] = array2[pos2];
pos2++;
pos3++;
continue;
}
if(pos2==array2.length){
array3[pos3] = array1[pos1];
pos1++;
pos3++;
continue;
}
if(array1[pos1]>array2[pos2]){
array3[pos3]=array2[pos2];
pos2++;
pos3++;
}else if(array1[pos1]<array2[pos2]){
array3[pos3]=array1[pos1];
pos1++;
pos3++;
}else{
array3[pos3]=array1[pos1];
pos1++;
pos2++;
pos3++;
}
}
array3 = removeZero(array3);
printArray("Merge result=",array3);
return array3;
}
}
}
private void checkIfArraySortedAsc(int[] arr){
if(arr==null||arr.length==0||arr.length==1){
return;
}else{
for(int i=1;i<arr.length;i++){
if(arr[i]<arr[i-1]){
throw new RuntimeException("Array ["+join(arr,",")+"] is not sorted desc!");
}
}
return;
}
}
/**
* 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<oldArray.length;i++){
newArr[i] = oldArray[i];
}
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){
if(max==1){
return new int[0];
}else if(max==2){
return new int[]{1,1};
}else{
int[] arr = new int[max];
arr[0]=1;
arr[1]=1;
int pos=2;
genFibonacci(arr,pos,max);
int[] result = removeZero(arr);
return result;
}
}
private void genFibonacci(int[] arr,int pos,int max){
int val = arr[pos-2]+arr[pos-1];
if(val<max){
arr[pos]=val;
pos++;
genFibonacci(arr,pos,max);
}else{
return;
}
}
/**
* 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){
int[] nonPrimeArr = new int[max];
int tmp;
//begin to calculate for nonPrime,start from 4 because 2 & 3 can not be calculated in this way
for(int i=2;i<max;i++){
for(int j=2;j<=i;j++){
tmp = i*j;
if(tmp<max){
//Mark as nonPrime numbers
nonPrimeArr[tmp]=1;
}else{
break;
}
}
}
int[] result = new int[max];
int pos = 0;
if(max>3){
result[pos]=2;
pos++;
}
if(max>4){
result[pos]=3;
pos++;
}
for(int i=4;i<nonPrimeArr.length;i++){
//for those value==0, mean indicated as Primes,index is the prime number
if(nonPrimeArr[i]==0){
result[pos]=i;
pos++;
}
}
result = removeZero(result);
return result;
}
/**
* 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<=1){
throw new RuntimeException("Invalid Arguement :max number="+max);
}else{
int[] result = new int[max];
int pos = 0;
for(int i=2;i<=max;i++){
int[] factors = getFactors(i);
int val =0;
//Sum of the factors
for(int j:factors){
val+=j;
}
//Check if the sum of factors equals to the number
if(val==i){
result[pos]=i;
pos++;
}
}
result = removeZero(result);
return result;
}
}
/**
* Get the factor of a integer
* @param num
* @return factors of this number as int array
*/
private int[] getFactors(int num){
int[] factors = new int[num];
int pos = 0;
for(int i=1;i<=num/2;i++){
if(num%i==0){
factors[pos]=i;
pos++;
}
}
return removeZero(factors);
}
/**
* 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: array){
if(sb.length()>0){
sb.append(seperator);
}
sb.append(i);
}
return sb.toString();
}
private void printArray(String msg,int[] array){
System.out.print(msg);
for(int i=0;i<array.length;i++){
System.out.print(array[i]+",");
}
System.out.println();
}
}