package com.donaldy.basic;
import java.util.ArrayList;
public class ArrayUtil {
private java.util.ArrayList arrayList;
private int[] newArr;
/**
* 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){
makeSure(origin);
/*int length = origin.length - 1;
int [] newArr = new int[length + 1];
for (int i = 0; i <= length; ++i)
newArr[i] = origin[length - i];
for (int i = 0 ; i <= length; ++i)
origin[i] = newArr[i];*/
for (int i = 0, j = origin.length - 1; i < j; ++i, --j) {
int t = origin[i];
origin[i] = origin[j];
origin[j] = t;
}
}
private void makeSure(int [] arr) {
if (arr.length == 0 || arr == null)
throw new RuntimeException();
}
/**
* 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){
makeSure(oldArray);
int length = oldArray.length;
arrayList = new ArrayList(length);
for (int i = 0; i < length ; ++i)
if (oldArray[i] != 0)
arrayList.add(oldArray[i]);
return toArray(arrayList.size());
}
private int[] toArray(int length) {
newArr = new int[length];
for (int i = 0; i < length ; ++i)
newArr[i] = (int)arrayList.get(i);
return newArr;
}
/**
* 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){
makeSure(array1);
makeSure(array2);
int length1 = array1.length;
int length2 = array2.length;
arrayList = new ArrayList(length1 + length2);
int i, j, cnt = 0, temp;
boolean flag = false;
for (i = 0, j = 0; i < length1 && j < length2; ) {
if (array1[i] < array2[j]) {
temp = array1[i];
i ++;
} else {
temp = array2[j];
j ++;
}
if (flag && temp != (int)arrayList.get(cnt)) {
arrayList.add(temp);
cnt ++;
} else if (!flag){
arrayList.add(temp);
flag = true;
}
}
for (i += 1; i < length1; ++i)
arrayList.add(array1[i]);
for (j += 1; j < length2; ++j)
arrayList.add(array2[j]);
return toArray(arrayList.size());
}
/**
* 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 + size;
newArr = new int[length];
int i = 0;
for (; i < oldArray.length ; ++i)
newArr[i] = oldArray[i];
for (; i < length; ++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) {
arrayList = new ArrayList();
arrayList.add(1);
arrayList.add(1);
int maxn = 2;
int i = 1;
while (maxn < max) {
arrayList.add(maxn);
i ++;
maxn = (int)arrayList.get(i) + (int)arrayList.get(i - 1);
}
;
return toArray(i + 1);
}
/**
* 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) {
arrayList = new ArrayList();
boolean prime[] = new boolean[max + 1];
int p = 0;
for (int i = 0; i < max; ++i)
prime[i] = true;
prime[0] = prime[1] = false;
for (int i = 2; i < max; ++i) {
if (prime[i]) {
arrayList.add(p ++, i);
for (int j = 2 * i; j < max; j += i)
prime[j] = false;
}
}
return toArray(arrayList.size());
}
/**
* 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) {
arrayList = new ArrayList();
int sum;
for (int i = 1; i < max; ++i) {
sum = 0;
for (int j = 1; j < i; ++j) {
if (i % j == 0)
sum += j;
}
if (sum == i)
arrayList.add(sum);
}
return toArray(arrayList.size());
}
/**
* 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){
StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append(array[0]);
for (int i = 1; i < array.length; ++i) {
stringBuilder.append(seperator + array[i]);
}
return stringBuilder.toString();
}
}