package com.github.lqingchenl.coding2017.array;
import org.junit.Test;
import java.util.HashMap;
import java.util.Map;
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[] b = new int[length];
for (int i = 0; i < length; i++) {
b[i] = origin[i];
}
for (int i = 0; i < length; i++) {
origin[length - i - 1] = b[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 int[] removeZero(int[] oldArray) {
if (oldArray == null) {
return null;
}
int length = oldArray.length;
for (int i : oldArray) {
if (i == 0) {
length--;
}
}
int[] newArray = new int[length];
int j = 0;
for (int i : oldArray) {
if (i != 0) {
newArray[j] = i;
j++;
}
}
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 == null || array1.length == 0) {
return array2;
}
if (array2 == null || array2.length == 0) {
return array1;
}
Map<Integer, Integer> map = new HashMap<>();
int sameNum = 0;
for (int i : array1) {
for (int j : array2) {
if (i == j) {
sameNum++;
map.put(i, 1);
}
}
}
int length = array1.length + array2.length - sameNum;
int[] newArray = new int[length];
int index = 0;
for (int i : array1) {
newArray[index] = i;
index++;
}
for (int j : array2) {
if (map.get(j) == null) {
newArray[index] = j;
index++;
}
}
for (int i = 0; i < newArray.length - 1; i++) {
for (int j = i + 1; j < newArray.length; j++) {
if (newArray[i] > newArray[j]) {
int temp = newArray[j];
newArray[j] = newArray[i];
newArray[i] = 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 int[] grow(int[] oldArray, int size) throws Exception {
if (oldArray == null) {
return null;
}
if (size < 0) {
throw new Exception("12");
}
int newLength = oldArray.length + size;
int[] newArray = new int[newLength];
for (int i = 0; i < newLength; i++) {
if (i < oldArray.length) {
newArray[i] = oldArray[i];
} else {
newArray[i] = 0;
}
}
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 int[] fibonacci(int max) {
if (max == 1) {
return new int[0];
}
int index = 0;
for (int i = 0; i < Integer.MAX_VALUE; i++) {
if (getFibonacci(i) > max) {
index = i;
break;
}
}
int[] array = new int[index];
for (int i = 0; i < index; i++) {
array[i] = getFibonacci(i);
}
return array;
}
/**
* 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 == 1) {
return new int[0];
}
int length = 0;
for (int i = 1; i <= max; i++) {
if (isPrime(i)) {
length++;
}
}
int[] array = new int[length];
int j = 0;
for (int i = 1; i <= max; i++) {
if (isPrime(i)) {
array[j] = i;
j++;
}
}
return array;
}
/**
* 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) {
StringBuffer stringBuffer = new StringBuffer();
for (int i = 1; i <= max; i++) {
int temp = 0;
for (int n = 1; n < i / 2 + 1; n++) {
if (i % n == 0) {
temp += n;
}
}
if (temp == i) {
stringBuffer.append(i).append("-");
}
}
String[] strArray = stringBuffer.toString().split("-");
int length = stringBuffer.toString().split("-").length;
int[] intAarray = new int[length];
for (int i=0; i<length; i++){
intAarray[i] = Integer.parseInt(strArray[i]);
}
return intAarray;
}
/**
* 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) {
if (array==null || array.length==0){
return "";
}
StringBuffer stringBuffer = new StringBuffer();
for (int i = 0; i<array.length; i++){
stringBuffer.append(array[i]);
if (i != array.length-1){
stringBuffer.append(seperator);
}
}
return stringBuffer.toString();
}
/**
* 获取斐波那契数列
*
* @param i
* @return
*/
private int getFibonacci(int i) {
if (i == 0 || i == 1) {
return 1;
}
return getFibonacci(i - 2) + getFibonacci(i - 1);
}
/**
* 判断是否为素数
*
* @param a
* @return
*/
private boolean isPrime(int a) {
boolean flag = true;
if (a < 2) {// 素数不小于2
return false;
} else {
for (int i = 2; i <= Math.sqrt(a); i++) {
if (a % i == 0) {// 若能被整除,则说明不是素数,返回false
flag = false;
break;// 跳出循环
}
}
}
return flag;
}
}