package lesson02;
import lesson01.ArrayList;
import lesson01.List;
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 len = origin.length;
int temp = 0;
for(int i = 0; i <= len >> 1; i++){
temp = origin[i];
origin[i] = origin[len - 1 - i];
origin[len - 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){
int count = 0;
for(int i = 0; i < oldArray.length; i++){
if(oldArray[i] != 0)
count++;
}
int[] arr = new int[count];
for(int i = oldArray.length - 1; i >= 0; i--){
if(oldArray[i] != 0)
arr[--count] = oldArray[i];
}
return arr;
}
/**
* 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 pos1 = 0;
int pos2 = 0;
ArrayList<Integer> al = new ArrayList<>();
while(pos1 < array1.length && pos2 < array2.length){
if(array1[pos1] > array2[pos2]){
al.add(array1[pos1]);
pos1++;
}else if(array1[pos1] < array2[pos2]){
al.add(array2[pos2]);
pos2++;
}else{
al.add(array1[pos1]);
pos1++;
pos2++;
}
}
while(pos1 < array1.length){
al.add(array1[pos1++]);
}
while(pos2 < array2.length){
al.add(array2[pos2++]);
}
int[] arr = W2P(al.toArray(new Integer[0]));
return arr;
}
private int[] W2P(Integer[] array) {
int[] arr = new int[array.length];
for(int i = 0; i < array.length; i++){
arr[i] = array[i].intValue();
}
return arr;
}
/**
* 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 len = oldArray.length;
int[] newArr = new int[len + size];
// for(int i = 0; i < len; i++){
// newArr[i] = oldArray[i];
// }
System.arraycopy(oldArray, 0, newArr, 0, len);
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 <= 0){
throw new IllegalArgumentException("Error argument:" + max);
}
if(max == 1){
return new int[0];
}else{
List<Integer> list = new ArrayList<>();
list.add(1);
list.add(1);
int count = 2;
int sum = 0;
while((sum = list.get(count - 1) + list.get(count - 2)) <= max){
list.add(sum);
count++;
}
return W2P((Integer[])list.toArray());
}
}
/**
* 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){
throw new IllegalArgumentException("Illegal argument:" + max);
}
List<Integer> list = new ArrayList<>();
for(int i = 2; i <= max; i++){
if(isPrimes(i))
list.add(i);
}
return W2P((Integer[])list.toArray());
}
private boolean isPrimes(int num) {
for(int i = 0; i <= Math.sqrt(num); i++){
if(num % 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){
if(max < 0){
throw new IllegalArgumentException();
}else{
List<Integer> list = new ArrayList<>();
list.add(0);
for(int i = 0; i < max; i++){
if(isPerfectNumber(i)){
list.add(i);
}
}
return W2P((Integer[])list.toArray());
}
}
private boolean isPerfectNumber(int num) {
int sum = 0;
for(int i = 1; i <= Math.sqrt(num); i++){
if(num % i == 0){
sum += i;
sum += num/i;
}
}
return sum == num;
}
/**
* 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){
int len = array.length;
if(len == 0){
return "";
}else{
StringBuilder sb = new StringBuilder();
sb.append(array[0]);
for(int i = 1; i < len; i++){
sb.append(seperator);
sb.append(array[i]);
}
return sb.toString();
}
}
}