package com.coding.basic.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 void reverseArray(int[] origin){
if(origin == null){
return;
}
int length = origin.length;
int i = 0;
int j = length - 1;
while (i < j){
int tmp = origin[i];
origin[i] = origin[j];
origin[j] = tmp;
i++;
j--;
}
}
/**
* 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 j = 0;
for (int i = 0; i < length; i++) {
if (oldArray[i] != 0){
newArray[j++] = oldArray[i];
}
}
int[] res = new int[j];
System.arraycopy(newArray, 0, res, 0, j);
return res;
}
/**
* 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];
}
if (array1 == null){
return array2;
}
if (array2 == null){
return array1;
}
int length1 = array1.length;
int length2 = array2.length;
int i = 0;
int j = 0;
int[] res = new int[length1 + length2];
int k = 0;
while (i < length1 || j < length2){
int next = Integer.MIN_VALUE;
if (i < length1 && j < length2){
if (array1[i] == array2[j]){
next = array1[i];
i++;
j++;
} else if (array1[i] < array2[j]){
next = array1[i++];
} else {
next = array2[j++];
}
} else if (i < length1){
next = array1[i++];
} else {
next = array2[j++];
}
if (k == 0){
res[k++] = next;
} else if (next > res[k-1]){
res[k++] = next;
}
}
int[] merged = new int[k];
System.arraycopy(res, 0, merged, 0, k);
return merged;
}
/**
* 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){
if (size < 0){
throw new IllegalArgumentException("illegal size");
}
int newLength = oldArray.length + size;
int[] newArray = new int[newLength];
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[] res = new int[max];
int i = 1;
int j = 1;
int k = 0;
res[k++] = 1;
res[k++] = 1;
int tmp = i + j;
while (tmp < max){
res[k++] = tmp;
i = j;
j = tmp;
tmp = i + j;
}
int[] result = new int[k];
System.arraycopy(res, 0, result, 0, k);
return result;
}
/**
* 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 < 3){
return new int[0];
}
int[] res = new int[max];
int k = 0;
for (int i = 2; i < max; i++) {
if (isPrime(i)){
res[k++] = i;
}
}
int[] result = new int[k];
System.arraycopy(res, 0, result, 0, k);
return result;
}
private boolean isPrime(int num){
if (num < 1){
return false;
}
for (int i = 2; i <= num / 2; i++) {
if (num % i == 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){
if (max < 0){
return new int[0];
}
int[] res = new int[max];
int k = 0;
for (int i = 0; i < max; i++) {
if (isPerfectNumbers(i)){
res[k++] = i;
}
}
int[] result = new int[k];
System.arraycopy(res, 0, result, 0, k);
return result;
}
private boolean isPerfectNumbers(int num){
return num == getFactorSum(num);
}
private int getFactorSum(int num){
if (num == 0 || num == 1){
return -1;
}
int sum = 0;
for (int i = 1; i <= num / 2; i++) {
if (num % i == 0){
sum += i;
}
}
return 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 separator
* @return
*/
public String join(int[] array, String separator){
if (array == null || array.length <= 0){
return "";
}
StringBuffer stringBuffer = new StringBuffer();
for (int i = 0; i < array.length - 1; i++) {
stringBuffer.append(String.valueOf(array[i])).append(separator);
}
stringBuffer.append(String.valueOf(array[array.length-1]));
return stringBuffer.toString();
}
public static void main(String[] args) {
ArrayUtil arrayUtil = new ArrayUtil();
System.out.println("-------------------------");
}
}