package com.github.fei9009.coderising0226.array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import com.sun.org.apache.bcel.internal.generic.ISTORE;
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 i = 0, j = origin.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){
if (oldArray == null || oldArray.length == 0){
return oldArray;
}
int count = 0;
for (int i = 0; i < oldArray.length; i++) {
if (oldArray[i] != 0) {
count++;
}
}
int[] newArray = new int[count];
int j = 0;
for (int i = 0; i <= oldArray.length - 1; i++) {
if (oldArray[i] == 0) {
continue;
}
newArray[j++] = oldArray[i];
}
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 && array2 == null) {
return null;
}
if (array1 == null) {
return array2;
}
if (array2 == null) {
return array1;
}
int i=0, j=0, k=0;
int len1 = array1.length;
int len2 = array2.length;
int[] mergeArr = new int[len1+len2];
while(true){
if(i == len1 || j == len2)
break;
if(array1[i]<array2[j]){
mergeArr[k++] = array1[i++];
}else if(array1[i]>array2[j]){
mergeArr[k++] = array2[j++];
}else{
mergeArr[k++] = array1[i++];
j++;
}
}
for(;i<len1;i++){
mergeArr[k++] = array1[i];
}
for(;j<len2;j++){
mergeArr[k++] = array2[j];
}
return Arrays.copyOfRange(mergeArr, 0, k);
}
/**
* 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 (oldArray == null) {
return null;
}
int[] newArr = new int[oldArray.length+size];
System.arraycopy(oldArray, 0,newArr, 0,oldArray.length);
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){
if (max == 1) {
return new int[]{};
}
List<Integer> list = new ArrayList<>();
int f1 = 1, f2 = 1, f3;
list.add(f1);
list.add(f2);
while (f1 +f2 < max) {
f3 = f1 + f2;
list.add(f3);
f1 = f2;
f2 = f3;
}
int[] result = new int[list.size()];
int j = 0;
for(Integer i : list) {
result[j++] = i;
}
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){
int[] a = new int[max];
int k=0;
for (int z = 1; z<max; z++){
int j = 1;
for (int i = 1; i<z; i++){
if(z%i == 0){
j++;
}
}
if(j == 2){
a[k++] = z;
}
}
return Arrays.copyOfRange(a,0,k);
}
/**
* 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){
int[] a = new int[max];
int k = 0;
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) {
a[k++] = i;
}
}
return Arrays.copyOfRange(a,0,k);
}
/**
* 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.length == 0) {
return "";
}
StringBuilder sb = new StringBuilder();
for (int i = 0; i < array.length - 1; i++) {
sb.append(Integer.toString(array[i]));
sb.append(seperator);
}
sb.append(Integer.toString(array[array.length-1]));
String result = sb.toString();
return result;
}
}