package com.coding.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 static void reverseArray(final int[] origin) {
int size = origin.length;
if (size <= 0) return;
int[] newArray = copyOf(origin);
for (int i = 0; i < size; i++) {
origin[i] = newArray[size - 1 - i];
}
}
/**
* 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 static int[] removeZero(int[] oldArray) {
int size = oldArray.length;
int countZero = 0;
//首先判断数组中0的个数
for (int i : oldArray) {
if (i == 0) countZero++;
}
int[] newArray = new int[size - countZero];
//cur 命名newArray的游标
int cur = 0;
for (int i = 0; i < size; i++) {
if (oldArray[i] == 0) continue;
newArray[cur++] = 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 static int[] merge(int[] array1, int[] array2) {
//判断数组是否为空
int size1 = array1.length;
int size2 = array2.length;
if (size1 <= 0 || size2 <= 0)
return size1 <= 0 ? array2 : array1;
//先将两个数组合并成一个数组
int[] newArray = new int[size1 + size2];
System.arraycopy(array1, 0, newArray, 0, size1);
System.arraycopy(array2, 0, newArray, size1, size2);
//对数组进行插入排序(假定array1已经是有序数组)
int in, out;
for (out = size1; out < newArray.length; out++) {
in = out;
int temp = newArray[out];
while (in > 0 && newArray[in - 1] >= temp) {
//右移
newArray[in] = newArray[in - 1];
--in;
}
newArray[in] = temp;
}
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 static int[] grow(int[] oldArray, int size) {
int oldSize = oldArray.length;
if (oldSize == 0) return new int[size];
if (size <= 0) return oldArray;
int[] newArray = new int[oldSize + size];
System.arraycopy(oldArray, 0, newArray, 0, oldSize);
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 static int[] fibonacci(int max) {
//先确定数组长度
if (max == 1) return new int[]{};
//这里的cur指的是数组的下标,从0开始,而不是数学函数1开始
int cur = 2;
int val_1 = 1;
int val_2 = 1;
while (val_1 + val_2 <= max) {
int temp = val_1;
val_1 = val_2;
val_2 += temp;
++cur;
}
int[] newArray = new int[cur];
for (int i = 0; i < cur; i++) {
if (i == 0 || i == 1) {
newArray[i] = 1;
continue;
}
newArray[i] = newArray[i - 1] + newArray[i - 2];
}
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 static int[] getPrimes(int max) {
//先确定数组长度
//判断质数循环
int count = 0;
for (int i = 1; i < max; i++) {
//去掉偶数
if (i == 1 || (i % 2 == 0 && i != 2)) continue;
boolean flag = true;
for (int j = 3; j <= Math.sqrt(i); j += 2) {
if (i % j == 0) {
flag = false;
break;
}
}
if (flag) count++;
}
int[] newArray = new int[count];
int cur = 0;
for (int i = 1; i < max; i++) {
//去掉偶数
if (i == 1 || (i % 2 == 0 && i != 2)) continue;
//判断到开根号即可
boolean flag = true;
for (int j = 3; j <= Math.sqrt(i); j += 2) {
if (i % j == 0) {
flag = false;
}
}
if (flag) {
newArray[cur] = i;
++cur;
}
}
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 static int[] getPerfectNumbers(int max) {
//求数组长度
int count = 0;
for (int a = 1; a <= max; a++) {
int sum = 0;
for (int i = 1; i <= a / 2; i++)
if (a % i == 0)
sum += i;
if (a == sum)
++count;
}
int[] newArray = new int[count];
int cur = 0;
for (int a = 1; a <= max; a++) {
int sum = 0;
for (int i = 1; i <= a / 2; i++)
if (a % i == 0)
sum += i;
if (a == sum) {
newArray[cur] = a;
++cur;
}
}
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 seperator
* @return
*/
public static String join(int[] array, String seperator) {
int size = array.length;
if (size == 0) return "";
StringBuffer sb = new StringBuffer("");
for (int i = 0; i < size - 1; i++) {
sb.append(array[i]).append(seperator);
}
sb.append(array[size - 1]);
return sb.toString();
}
/**
* 类私有函数,复制返回一个新的数组
*/
private static int[] copyOf(int[] source) {
int size = source.length;
if (size <= 0) return null;
int[] newArray = new int[size];
//int[] ints = Arrays.copyOf(origin, size);
System.arraycopy(source, 0, newArray, 0, size);
return newArray;
}
}