package com.coderising.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){
int first = 0;
int last = origin.length - 1;
while (first < last) {
int temp;
temp = origin[first];
origin[first] = origin[last];
origin[last] = temp;
first++;
last--;
}
}
/**
* 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){
// count how many zeros
int zeroCount = 0;
int len= oldArray.length;
if (len==0) {
return new int[]{};
}
for (int i=0; i<len; i++) {
if (oldArray[i]==0) {
zeroCount++;
}
}
if (zeroCount == 0) {
return oldArray;
}
// create a new array
int newLen = len - zeroCount;
int[] newArr = new int[newLen];
// copy to the new array and return
int k = 0;
for (int j=0; j<len; j++) {
if (oldArray[j]!=0) {
newArr[k] = oldArray[j];
k++;
}
}
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){
int len1 = array1.length;
int len2 = array2.length;
int newSize = len1+len2;
int[] newArray = new int[newSize];
int i = 0; // i for array1
int j = 0; // j for array2
int k = 0; // k for newArray
while(i <=len1-1 && j<=len2-1) {
if (array1[i] < array2[j]) {
newArray[k++] = array1[i];
i++;
} else if (array1[i] == array2[j]){
newArray[k++] = array1[i];
newArray[k++] = 0;
i++;
j++;
} else {
newArray[k++] = array2[j];
j++;
}
}
while(i<len1) {
newArray[k++] = array1[i++];
}
while(j<len2) {
newArray[k++] = array2[j++];
}
// remove 0 after merge
return this.removeZero(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 len = oldArray.length;
if (len ==0) {
return new int[]{};
}
int newSize = len + size;
int[] newArray = new int[newSize];
for(int i=0; i<len; i++) {
newArray[i] = oldArray[i];
}
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[]{};
}
int[] arr = new int[max];
arr[0] = 1;
arr[1] = 1;
int k = 2;
do {
arr[k] = arr[k-1] + arr[k-2];
} while(arr[k++]<=max);
// remove the last element since the condition exit
// when it is already passed the limit
arr[k-1] = 0;
return this.removeZero(arr);
}
/**
* 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[] primes = new int[max];
for(int i=0; i<primes.length; i++) {
primes[i] = i;
}
// we know 0 and 1 are not prime
primes[0] = 0;
primes[1] = 0;
for (int i=2; i<primes.length; i++) {
// if value is prime, all it's multiplier is prime and set to 0
if(primes[i] !=0) {
for(int j=2; j<primes.length; j++) {
if(i*j < max) {
primes[i*j] = 0;
}
}
}
}
return this.removeZero(primes);
}
/**
* 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==1) {
return new int[]{};
}
int[] newArr = new int[max];
int k =0;
int sum=0;
for (int i=1; i<=max;i++) {
for(int j=1; j<i;j++) {
if(i%j ==0) {
sum+=j;
}
}
if(sum==i) {
newArr[k++] = i;
}
sum=0;
}
return this.removeZero(newArr);
}
/**
* 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){
if (array==null) {
return null;
}
final int noOfItems = array.length;
final StringBuilder buf = new StringBuilder(noOfItems * 16);
for (int i =0; i<noOfItems; i++) {
buf.append(Integer.toString(array[i]));
if (i!=noOfItems-1 && seperator!=null) {
buf.append(seperator);
}
}
return buf.toString();
}
}