package coderising.array;
public class ArrayUtil {
private void checkArray(int[] origin) {
if (origin == null) {
throw new NullPointerException("array is null refresh ");
}
}
/**
* 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]
* 4 9 30 3 7
* 4 3 30 9 7
*
* @param origin
* @return
*/
public void reverseArray(int[] origin) {
if (origin.length < 2) {
return;
}
for (int i = 0; i < origin.length / 2; i++) {
int temp = origin[i];
origin[i] = origin[origin.length - i - 1];
origin[origin.length - i - 1] = 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) {
checkArray(oldArray);
int[] newArr = new int[oldArray.length];
int index = 0;
for (int i = 0; i < oldArray.length; i++) {
if (oldArray[i] != 0) {
newArr[index] = oldArray[i];
index++;
}
}
int[] newArrs = new int[index];
System.arraycopy(newArr, 0, newArrs, 0, index);
return newArrs;
}
/**
* 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 new int[0];
} else if (array1 == null || array1.length < 1) {
return array2;
} else if (array2 == null || array2.length < 1) {
return array1;
}
int index1 = 0;
int index2 = 0;
int index = 0;
int[] tempArr = new int[array1.length + array2.length];
for (int i = index1; i < tempArr.length; i++) {
for (int j = index2; j < array2.length; j++) {
int i1 = array1[index1];
int i2 = array2[index2];
if (i1 > i2) {
tempArr[index] = i2;
index2 = index2 + 1;
index++;
break;
} else if (i1 < i2) {
tempArr[index] = i1;
index1 = index1 + 1;
index++;
break;
} else {
tempArr[index] = i1;
index1 = index1 + 1;
index2 = index2 + 1;
index++;
break;
}
}
if (index2 >= array2.length && index1 < array1.length) {
tempArr[index] = array1[index1];
index1 = index1 + 1;
index++;
}
}
int[] newArr = new int[index];
System.arraycopy(tempArr, 0, newArr, 0, index);
return newArr;
}
/**
* 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) {
int[] tempArray = new int[max];
int[] ints = new int[0];
for (int i = 1; i <= max; i++) {
int num = fibonacci1(i);
if (num < max) {
tempArray[i - 1] = num;
} else {
ints = new int[i - 1];
System.arraycopy(tempArray, 0, ints, 0, i - 1);
break;
}
}
return ints;
}
// 递归实现方式
public static int fibonacci1(int n) {
if (n <= 2) {
return 1;
} else {
return fibonacci1(n - 1) + fibonacci1(n - 2);
}
}
/**
* 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 i, j, index = 0;
int[] tempArray = new int[max];
for (i = 1; i <= max; i++) {
for (j = 2; j < i; j++)
if (i % j == 0) break;
if (j < i)
continue;
else {
tempArray[index] = i;
index++;
System.out.println(i);
}
}
int[] arr = new int[index];
System.arraycopy(tempArray, 0, arr, 0, index);
return arr;
}
/**
* 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) {
int sum = 0, i, j, index = 0;
int[] tempArray = new int[max];
for (i = 1; i <= max; i++) {
for (j = 1, sum = 0; j <= i / 2; j++) {
if (i % j == 0)
sum += j;
}
if (sum == i) {
System.out.println("完数:" + i);
tempArray[index] = i;
index++;
}
}
int[] arr = new int[index];
System.arraycopy(tempArray, 0, arr, 0, index);
return arr;
}
/**
* 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 seperator
* @return
*/
public String join(int[] array, String seperator) {
StringBuilder stringBuilder = new StringBuilder();
for (int i = 0; i < array.length; i++) {
stringBuilder.append(i);
if (i != array.length - 1) {
stringBuilder.append(seperator);
}
}
System.out.println("stringBuilder = " + stringBuilder.toString());
return stringBuilder.toString();
}
}