package com.coderising.array;
import java.util.ArrayList;
import java.util.List;
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 len = origin.length;
for (int i = 0; i < len/2; i++) {
int temp = origin[i];
origin[i] = origin[len-1-i];
origin[len-1-i] = temp;
}
}
/**
* 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 slow = 0;
for (int i = 0; i < oldArray.length; i++) {
if (oldArray[i] != 0) {
oldArray[slow++] = oldArray[i];
}
}
int[] newArray = new int[slow];
for (int i = 0; i < slow; i++) {
newArray[i] = 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){
int[] result = new int[array1.length + array2.length];
int i1 = 0 , i2 = 0, i3 = 0;
while (i1 < array1.length && i2 < array2.length) {
if (array1[i1] == array2[i2]) {
result[i3++] = array1[i1++];
i2++;
} else if (array1[i1] < array2[i2]) {
result[i3++] = array1[i1++];
} else {
result[i3++] = array2[i2++];
}
}
while (i1 < array1.length) {
result[i3++] = array1[i1++];
}
while (i2 < array2.length) {
result[i3++] = array2[i2++];
}
int[] finalResult = new int[i3];
for (int i = 0; i < i3; i++) {
finalResult[i] = result[i];
}
return finalResult;
}
/**
* 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[] result = new int[oldArray.length + size];
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 int[] fibonacci(int max){
List<Integer> result = new ArrayList<>();
if (max <= 1) return new int[]{};
if (max < 2) return new int[]{1,1};
result.add(1);
//result.add(1);
int num = 1, index = 1;
while (num < max) {
result.add(num);
num = result.get(index) + result.get(index - 1);
index++;
}
int[] resArray = new int[result.size()];
for (int i = 0; i < result.size(); i++) {
resArray[i] = result.get(i);
}
return resArray;
}
/**
* 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){
List<Integer> result = new ArrayList<>();
boolean[] notPrime = new boolean[max];
for (int i = 2; i < max; i++) {
if (!notPrime[i]) result.add(i);
for (int j = 2; i*j < max; j++) {
notPrime[i*j] = true;
}
}
int[] resArray = new int[result.size()];
for (int i = 0; i < result.size();i++) {
resArray[i] = result.get(i);
}
return resArray;
}
/**
* 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){
List<Integer> result = new ArrayList<>();
for (int i = 1; i < max; i++) {
int sum = 0;
for (int j = 1; j < i/2; j++) {
if (i % j == 0) {
sum += j;
}
}
if (sum == i) result.add(i);
}
int[] resArray = new int[result.size()];
for (int i = 0; i < result.size(); i++) {
resArray[i] = result.get(i);
}
return resArray;
}
/**
* 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 || array.length == 0) return null;
int len = array.length;
char[] result = new char[len + seperator.length()*(len - 1)];
int indexA = 0, indexR = 0;
while (indexA < array.length && indexR < result.length) {
result[indexR++] = (char)array[indexA++];
if (indexA < array.length - 1){
for (int i = 0; i < seperator.length(); i++) {
result[indexR++] = seperator.charAt(i);
}
}
}
return String.valueOf(result);
}
}