package me.lzb.basic.list;
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[] target = new int[origin.length];
for (int i = 0; i < origin.length; i++) {
target[i] = origin[origin.length - 1 - i];
}
origin = target;
}
/**
* 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 l = 0;
for (int i = 0; i < oldArray.length; i++) {
if (oldArray[i] != 0) {
l = l + 1;
}
}
int[] target = new int[l];
int a = 0;
for (int i = 0; i < oldArray.length; i++) {
if (oldArray[i] != 0) {
target[a] = oldArray[i];
a = a + 1;
}
}
return target;
}
/**
* 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
*/
//一个一个放进去,循环次数有点多
public int[] merge(int[] array1, int[] array2) {
int[] tmp = new int[array1.length + array2.length];
int mini = 0;
int a1 = array1[0];
int a2 = array2[0];
if(a1 < a2){
mini = a1;
}else {
mini = a2;
}
tmp[0] = mini;
int l3 = 0;
for (int i = 1; i < array1.length + array2.length; i++) {
// if(mini >= array1[l1 - 1] && mini >= array2[l2 - 1]){
// l3 = i;
// break;
// }
int oldMin = mini;
int aa1 = mini;
if(mini < array1[array1.length - 1] ){
for (int j = 0; j < array1.length; j++) {
if(array1[j] > mini){
aa1 = array1[j];
break;
}
}
}
int aa2 = mini;
if(mini < array2[array2.length - 1] ){
for (int j = 0; j < array2.length; j++) {
if(array2[j] > mini){
aa2 = array2[j];
break;
}
}
}
if(aa1 != oldMin && aa2 != oldMin){
if(aa1 < aa2){
mini = aa1;
}else {
mini = aa2;
}
}else if(aa1 != oldMin){
mini = aa1;
}else {
mini = aa2;
}
if(oldMin == mini){
l3 = i;
break;
}
tmp[i] = mini;
}
int[] result = new int[l3];
System.arraycopy(tmp, 0, result, 0, l3);
return result;
}
/**
* 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 newArray[] = new int[oldArray.length + size];
System.arraycopy(oldArray, 0, newArray, 0, oldArray.length);
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[] result = {1, 1};
int i = 2;
int n = 0;
while (n < max){
int[] t = new int[result.length + 1];
System.arraycopy(result, 0, t, 0, result.length);
n = t[i-1] + t[i - 2];
if(n >= max){
return result;
}
t[i] = n;
result = t;
i = i + 1;
}
return null;
}
/**
* 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];
}
if (max == 3){
return new int[]{2};
}
int[] primes = new int[max+1];
primes[0] = 2;
int count = 1;
for (int i = 3; i < max; i = i + 2) {
boolean isPrime = true;
for (int j = 3; j < i; j++) {
if(i % j == 0){
isPrime = false;
break;
}
}
if(isPrime){
primes[count] = i;
count = count + 1;
}
}
int[] result = new int[count];
System.arraycopy(primes, 0, result, 0, count);
return result;
}
private boolean isPrime(int a){
if (a < 2) {
return false;
}
if (a == 2) {
return true;
}
if(a % 2 == 0){
return false;
}
for (int i = 3; i < a; i = i + 2) {
if(a % i == 0){
return false;
}
}
return true;
}
/**
* 所谓“完数”, 是指这个数恰好等于它的真因子之和,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[] pns = new int[max];
int count = 0;
for (int i = 6; i < max; i++) {
if (isPerfectNumber(i)){
pns[count] = i;
count = count + 1;
}
}
int[] result = new int[count];
System.arraycopy(pns, 0, result, 0, count);
return result;
}
private boolean isPerfectNumber(int a){
if(a < 6){
return false;
}
int sum = 0;
for (int i = 1; i < a; i++) {
if(a % i == 0){
sum = sum + i;
}
}
return sum == a;
}
/**
* 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
* @return
*/
public static String join(int[] array, String seperator) {
String result = "";
for (int i = 0; i < array.length; i++) {
result = result + array[i] + seperator ;
}
result = result.substring(0, result.length() - 1);
return result;
}
}