package main.week02.practice;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import com.sun.xml.internal.ws.org.objectweb.asm.Label;
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.length <= 1) {
return;
}
int i = 0, j = origin.length - 1;
while (j > i) {
origin[i] = origin[i] ^ origin[j];
origin[j] = origin[i] ^ origin[j];
origin[i] = origin[i] ^ origin[j];
i++;
j--;
}
}
/**
* 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 i = 0;
for (int j = 0; j < oldArray.length; j++) {
if (0 != oldArray[j]) {
oldArray[i++] = oldArray[j];
}
}
int[] newArray = new int[i];
System.arraycopy(oldArray, 0, newArray, 0, newArray.length);
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.length == 0) {
return array2;
}
if (array2.length == 0) {
return array1;
}
int n = 0;
int[] merge = new int[array1.length + array2.length];
int i = 0, j = 0;
while (i < array1.length || j < array2.length) {
if (array1[i] == array2[j]) {
merge[n] = array1[i];
n++;
i++;
j++;
if (i == array1.length) {
System.arraycopy(array2, j, merge, n, array2.length - j);
n += array2.length - j;
break;
}
if (j == array2.length) {
System.arraycopy(array1, i, merge, n, array1.length - i);
n += array1.length - i;
break;
}
continue;
}
if (array1[i] < array2[j]) {
merge[n] = array1[i];
n++;
i++;
if (i == array1.length) {
System.arraycopy(array2, j, merge, n, array2.length - j);
n += array2.length - j;
break;
}
} else {
merge[n] = array2[j];
n++;
j++;
if (j == array2.length) {
System.arraycopy(array1, i, merge, n, array1.length - i);
n += array1.length - i;
break;
}
}
}
int[] res = new int[n];
System.arraycopy(merge, 0, res, 0, n);
return res;
}
/**
* 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[] res = new int[oldArray.length + size];
System.arraycopy(oldArray, 0, res, 0, oldArray.length);
return res;
}
/**
* 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];
}
if(max == 2){
return new int[]{1,1};
}
int[] arr = new int[max];
arr[0] = arr[1] = 1;
int count = 2;
for(; count < max; count++){
arr[count] = arr[count-1] + arr[count-2];
if(arr[count] >= max){
break;
}
}
return Arrays.copyOf(arr, count);
// ArrayList<Integer> list = new ArrayList<Integer>();
// list.add(1);
// list.add(1);
// int index = 1;
// while (list.get(index) + list.get(index - 1) < max) {
// list.add(list.get(index) + list.get(index - 1));
// index++;
// }
// Iterator<Integer> iter = list.iterator();
// int[] res = new int[list.size()];
// int i = 0;
// while (iter.hasNext()) {
// res[i++] = iter.next();
// }
// return res;
}
/**
* 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 new int[0];
}
int n = 2;
int arr[] = new int[max];
int j = 0;
a: for (; n < max; n++) {
for (int i = 2; i < n / 2 + 1; i++) {
if (n % i == 0)
continue a;
}
arr[j++] = n;
}
int[] res = new int[j];
System.arraycopy(arr, 0, res, 0, j);
return res;
}
/**
* 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 new int[0];
}
int n = 6, sum = 0, j = 0;
int[] arr = new int[max];
for (; n < max; n++, sum = 0) {
for (int i = 1; i < n / 2 + 1; i++) {
if (n % i == 0)
sum += i;
}
if (sum == n)
arr[j++] = n;
}
int[] res = new int[j];
System.arraycopy(arr, 0, res, 0, j);
return res;
}
/**
* 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 (array.length == 0) {
return "";
}
StringBuilder sb = new StringBuilder();
int i;
for (i = 0; i < array.length - 1; i++) {
sb.append(array[i]);
sb.append(seperator);
}
sb.append(array[i]);
return sb.toString();
}
}