package com.basic;
import java.util.Collections;
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 length = origin.length;
int left = 0;
int right = length - 1;
int a = 0;
int b = 0;
while (left < right) {
swap(origin, left++, right--);
}
}
private void swap(int[] origin, int i, int j) {
// TODO Auto-generated method stub
int tmp = origin[i];
origin[i] = origin[j];
origin[j] = tmp;
}
/**
* 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 length = oldArray.length;
int[] newArray = new int[length];
int[] zeroArray = new int[length];
int zIndex = 0;
int nzIndex = 0;
for (int i = 0; i < length; i++) {
if (oldArray[i] == 0) {
zeroArray[zIndex++] = oldArray[i];
} else {
newArray[nzIndex++] = oldArray[i];
}
}
int[] newArray2 = new int[nzIndex];
for (int i = 0; i < nzIndex; i++) {
newArray2[i] = newArray[i];
}
return newArray2;
}
/**
* 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 length1 = array1.length;
int length2 = array2.length;
int[] array3 = new int[length1 + length2];
int index1 = 0;
int index2 = 0;
int index3 = 0;
while (index1 < length1 && index2 < length2) {
if (index3 > 0) {
if (array3[index3 - 1] == array1[index1]) {
++index1;
continue;
}
if (array3[index3 - 1] == array2[index2]) {
++index2;
continue;
}
}
if (array1[index1] == array2[index2]) {
array3[index3++] = array1[index1];
++index1;
++index2;
continue;
}
if (array1[index1] < array2[index2]) {
array3[index3++] = array1[index1];
++index1;
continue;
}
if (array1[index1] > array2[index2]) {
array3[index3++] = array2[index2];
++index2;
continue;
}
}
while (index1 < length1) {
array3[index3++] = array1[index1++];
}
while (index2 < length2) {
array3[index3++] = array1[index2++];
}
int[] newArray = new int[index3];
for (int i = 0; i < index3; i++) {
newArray[i] = array3[i];
}
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 int[] grow(int[] oldArray, int size) {
int length = oldArray.length;
int[] newArr = new int[length + size];
for (int i = 0; i < length; i++) {
newArr[i] = oldArray[i];
}
for (int i = length; i < length + size; i++) {
newArr[i] = 0;
}
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 == 1) {
return null;
}
int[] arr = new int[max / 2];
int a = 1;
int b = 1;
int c = 0;
arr[0] = 1;
arr[1] = 1;
int index = 2;
while (a + b < max) {
arr[index++] = a + b;
c = b;
b = a + b;
a = c;
}
int[] newArr = new int[index];
for (int i = 0; i < index; i++) {
newArr[i] = arr[i];
}
return newArr;
}
/**
* 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 size = max / 2 + 1;
int[] arr = new int[size];
int index = 0;
for (int i = 2; i < max; i++) {
if (isPrime(i)) {
arr[index++] = i;
}
}
int[] newArr = new int[index];
for (int i = 0; i < index; i++) {
newArr[i] = arr[i];
}
return newArr;
}
public boolean isPrime(int i) {
for (int j = 2; j < i / 2; j++) {
if (i % j == 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) {
int size = max / 2 + 1;
int[] arr = new int[size];
int index = 0;
for (int i = 2; i < max; i++) {
if (isPerfectNumber(i)) {
arr[index++] = i;
}
}
int[] newArr = new int[index];
for (int i = 0; i < index; i++) {
newArr[i] = arr[i];
}
return newArr;
}
public boolean isPerfectNumber(int num) {
int sum = 0;
for (int i = 1; i <= num / 2; i++) {
if (num % i == 0) {
sum += i;
}
}
// System.out.println("num: " + num + ", sum:" + sum);
return (num == sum);
}
/**
* 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 str = "";
int length = array.length;
for (int a : array) {
str += a + seperator;
}
str = str.substring(0, str.length() - 1);
return str;
}
}