package com.coding.basic.homework_02.array;
import java.util.Arrays;
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
*/
public static void reverseArray(int [] origin){
if(origin.length > 1){ // 数组的长度大于1置换才有意义
int tem;
for(int i = 0; i < origin.length / 2; i++){
tem = origin[i];
origin[i] = origin[origin.length - 1 - i];
origin[origin.length - 1 - i] = tem;
}
}
}
/**
* 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 static int[] removeZero(int[] oldArray){
int len = 0;
for(int i : oldArray){
if(i == 0)
continue;
len++;
}
int[] result = new int[len];
len = 0;
for(int i = 0; i < oldArray.length; i++){
if(oldArray[i] == 0)
continue;
result[len++] = oldArray[i];
}
return result;
}
/**
* 给定两个已经排序好的整形数组 a1,a2,创建一个新的数组a3,使得a3包含a1和a2的所有元素并集
* 例如a1 = [3,5,7,8] , a2 = [4,5,6,7] 则a3为[3,4,5,6,7,8]
* @param array1
* @param array2
* @return
*/
public static int [] merge(int[] array1, int [] array2){
if(array1.length == 0)
return array2;
if(array2.length == 0)
return array1;
if(array1.length == 0 && array2.length == 0)
return null;
int arrLen1 = 0;
int arrLen2 = 0;
int arrLen3 = 0;
int []result = new int[array1.length + array2.length];
while(arrLen1 < array1.length || arrLen2 < array2.length){
if(arrLen1 >= array1.length){ //数组1已经没了
result[arrLen3++] = array2[arrLen2++];
continue;
}
if(arrLen2 >= array2.length){ //数组2已经没了
result[arrLen3++] = array1[arrLen1++];
continue;
}
if(array1[arrLen1] > array2[arrLen2]){
result[arrLen3++] = array2[arrLen2++];
}else if(array1[arrLen1] < array2[arrLen2]){
result[arrLen3++] = array1[arrLen1++];
}else{
result[arrLen3++] = array1[arrLen1++];
arrLen2++;
}
}
result = Arrays.copyOf(result, arrLen3);
return result;
}
/**
* 把一个已经存满数据的数组oldArray的容量进行扩容，扩容后的新数据大小为oldArray.length * 2
* 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 static int[] grow(int[] oldArray, int size){
int[] result = new int [size * 2];
for(int i = 0; i < oldArray.length; i++){
result[i] = oldArray[i];
}
return result;
}
/**
* 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 static int[] fibonacci(int max){
if(max == 1)
return new int[]{};
int[] result = new int[10];
int reLen = 2;
result[0] = result[1] = 1;
while(result[reLen - 1] + result[reLen -2] < max){
if(reLen >= result.length)
result = grow(result, result.length);
result[reLen] = result[reLen - 1] + result[reLen -2];
reLen++;
}
result = Arrays.copyOf(result, reLen);
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 static int[] getPrimes(int max){
if(max <= 2){
return null;
}
int[] result = new int[10];
int len = 0;
boolean flag = true;
result[0] = 2;
if(max == 3)
return result;
len++;
for(int i = 3; i < max; i++){
flag = true;
if(len >= result.length)
result = grow(result, result.length);
for(int j = 2; j < i; j++){
if(i % j == 0){
flag = false;
}
}
if(flag == true){
result[len++] = i;
}
}
result = Arrays.copyOf(result, len);
return result;
}
/**
* 所谓"完数"，是指这个数恰好等于他的因子之和，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 static int[] getPerfectNumbers(int max){
int sum = 1;
int [] result = new int[10];
int len = 0;
for(int i = 2;i < max; i++){
sum = 1;
if(len >= result.length)
result = grow(result, result.length);
for(int j = 2; j < i; j++){
if(i % j == 0)
sum += j;
}
if(sum == i)
result[len++] = sum;
}
result = Arrays.copyOf(result, len);
return result;
}
/**
* 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 static String join(int[]array, String seperator){
String result = new String();
int len = 0;
result = new Integer(array[0]).toString();
for(int i = 1; i < array.length; i++){
result += seperator;
result += array[i];
}
return result;
}
}