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(checkArrayIsNull(origin)){
return;
}
int size = origin.length;
for (int i = 0; i < size/2; i++) {
int swap = origin[i];
origin[i] = origin[size - 1 - i];
origin[size - 1 - i] = swap;
}
}
/**
* 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(checkArrayIsNull(oldArray)){
return null;
}
int[] swap = new int [oldArray.length];
int size = 0;
for (int i = 0; i < oldArray.length; i++) {
if(oldArray[i] == 0){
continue;
}
swap[size] = oldArray[i];
++size;
}
int[] newArray = new int[size];
System.arraycopy(swap, 0, newArray, 0, size);
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(checkArrayIsNull(array1) && checkArrayIsNull(array2)){
return null;
}
int[] swap = new int[array1.length + array2.length];
int index1 = 0,index2 = 0,size = 0;
while(index1 < array1.length && index2 < array2.length){
if(array1[index1] == array2[index2]){
swap[size++] = array1[index1];
++index1;
++index2;
}else if(array1[index1] < array2[index2]){
if(size > 0 && swap[size-1] == array1[index1]){
++index1;
continue;
}
swap[size++] = array1[index1++];
}else{
if(size > 0 && swap[size-1] == array2[index2]){
++index2;
continue;
}
swap[size++] = array2[index2++];
}
}
while(index1 < array1.length){
swap[size++] = array1[index1];
++index1;
}
while(index2 < array2.length){
swap[size++] = array2[index2];
++index2;
}
int[] newArray = new int [size];
System.arraycopy(swap, 0, newArray, 0, size);
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(checkArrayIsNull(oldArray)){
return null;
}
int length = oldArray.length;
int[] newArray = new int [length + size];
System.arraycopy(oldArray, 0, newArray, 0, 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){
return null;
}
if(max == 1){
return new int[0];
}
int array[] = null;
if(max < 20 ){
array = new int [max];
}else{
array =new int [max/2];
}
array[0] = array[1] = 1;
int index = 1;
while(array[index-1] + array[index] < max){
array[index+1] = array[index-1] + array[index];
++index;
}
int[] newArray = new int [index+1];
System.arraycopy(array, 0, newArray, 0, index+1);
return newArray;
}
/**
* 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;
}
int init = 2;
int size = 0;
int array[] = new int[max];
boolean flag = true;
while(init < max){
flag = true;
for (int i = 2; i < init; i++) {
if(init % i == 0){
flag = false;
break;
}
}
if(flag){
array[size++] = init;
}
++init;
}
int[] newArray = new int [size];
System.arraycopy(array, 0, newArray, 0, size);
return newArray;
}
/**
* 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;
}
int array[] = new int[max];
int init = 6;
int size = 0,sum = 0;
while(init < max){
sum = 0;
for (int i = 1; i <= init/2; i++) {
if(init % i == 0){
sum += i;
}
}
if(sum == init){
array[size++] = init;
}
++init;
}
int[] newArray = new int [size];
System.arraycopy(array, 0, newArray, 0, size);
return newArray;
}
/**
* 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){
if(checkArrayIsNull(array) || seperator == null){
return null;
}
StringBuilder stringBuilder = new StringBuilder();
int size = array.length;
for (int i = 0; i < size; i++) {
if(i != size - 1){
stringBuilder.append(array[i]).append(seperator);
continue;
}
stringBuilder.append(array[i]);
}
return stringBuilder.toString();
}
private boolean checkArrayIsNull(int[] array){
if(array == null){
return true;
}
return false;
}
}