package com.coderising.array;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
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 int[] reverseArray(int[] origin){
if(origin == null)
return null;
int length = origin.length;
int[] target = new int[length];
for(int i=0; i<length ;i++){
target[length-1-i] = origin[i];
}
return target;
}
/**
* 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)
return null;
int zeroNum = 0;
int length = oldArray.length;
for(int i=0; i<length; i++){
if(oldArray[i] == 0)
zeroNum++;
}
int[] newArray = new int[length - zeroNum];
int j = 0;
for(int i=0; i<length; i++){
if(oldArray[i] != 0)
newArray[j++] = oldArray[i];
}
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(array1 == null || array2 == null)
return array1 == null ? array2 : array1;
Set<Integer> set = new HashSet<Integer>();
for(int i=0; i<array1.length; i++){
set.add(array1[i]);
}
for(int i=0; i<array2.length; i++){
set.add(array2[i]);
}
int[] target = new int[set.size()];
int i = 0;
Iterator<Integer> it = set.iterator();
while(it.hasNext()){
target[i++] = it.next();
}
return target;
}
/**
* 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(oldArray == null)
return null;
if(size == 0)
return oldArray;
if(size < 0)
throw new RuntimeException("参数错误");
int length = oldArray.length + size;
int[] target = new int[length];
System.arraycopy(oldArray, 0, target, 0, oldArray.length);
for(int i=oldArray.length; i< length; i++){
target[i] = 0;
}
return target;
}
/**
* 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)
throw new RuntimeException("参数错误");
if(max == 1){
int[] result = {};
return result;
}
if(max == 2){
int[] result = {1, 1};
return result;
}
List<Integer> list = new ArrayList<Integer>();
list.add(1);
list.add(1);
for(int i=2; ; i++){
int tmp = list.get(i-2) + list.get(i-1);
if(tmp < max){
list.add(tmp);
}else{
break;
}
}
int size = list.size();
int[] result = new int[size];
for(int i=0; i<size; i++)
result[i] = list.get(i);
return result;
}
/**
* 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 <= 0)
throw new RuntimeException("参数错误");
if(max <=2 ){
int[] result = {};
return result;
}
if(max <= 13){
int[] tmp = {2,3,5,7,11,13};
int index = 0;
for(int i=0; i<6; i++){
index = i;
if(tmp[i] >= max)
break;
}
int[] result = new int[index];
System.arraycopy(tmp, 0, result, 0, index);
return result;
}
List<Integer> list = new ArrayList<Integer>();
list.add(2);
list.add(3);
list.add(5);
list.add(7);
list.add(11);
for(int i=13; i<max; i+=2){
boolean isNum = true;
for(int j=3; j<=Math.sqrt(i); j++){
if(i%j == 0){
isNum = false;
break;
}
}
if(isNum == true)
list.add(i);
}
int[] result = new int[list.size()];
for(int i=0; i<list.size(); i++)
result[i] = list.get(i);
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("参数错误");
if(max <= 5){
int[] result = {};
return result;
}
List<Integer> list = new ArrayList<Integer>();
for(int input = 2; input<max; input++){
int sum = 1;
for(int i=2; i<=input/2.0; i++){
if(input % i == 0){
sum += i;
}
}
if(sum == input)
list.add(input);
}
int[] result = new int[list.size()];
for(int i=0; i<list.size(); i++)
result[i] = list.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 String join(int[] array, String seperator){
String s = "";
for(int i=0; i<array.length-1; i++){
s = s + (array[i]) + "-";
}
s = s + array[array.length-1];
return s;
}
}