/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package javaclass;
import java.util.Arrays;
/**
*
* @author CJ
*/
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 totalLen = origin.length;
int[] revIntArr = new int[totalLen];
for (int i = 0; i < totalLen; i++) {
revIntArr[i] = origin[totalLen - 1 - i];
}
for (int i = 0; i < totalLen; i++) {
origin[i] = revIntArr[i];
}
}
/**
* 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 totalLen = oldArray.length;
int[] tmpArr = new int[totalLen];
int nonZeroCount = 0;
for (int i : oldArray) {
if (i != 0) {
tmpArr[nonZeroCount++] = i;
}
}
return Arrays.copyOfRange(tmpArr, 0, nonZeroCount);
}
/**
* 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) {
// 不考虑 寻址
// 不考虑效率
int arrLen1 = array1.length;
int arrLen2 = array2.length;
int maxLen = arrLen1+arrLen2;
int[] mergedArr = new int[maxLen];
int mergedC = 0;
int i = 0;
int j = 0;
while(i<arrLen1 && j<arrLen2){
int cur1 = array1[i];
while(j<arrLen2){
int cur2 = array2[j];
if(cur1<cur2){
mergedArr[mergedC++] = cur1;
break;
}else if(cur1==cur2){
mergedArr[mergedC++] = cur1;
j++;
break;
}else{
mergedArr[mergedC++] = cur2;
}
j++;
}
i++;
}
// 补齐 没有迭代完的数组,因为这个出现了长度差别
while(i<arrLen1){
mergedArr[mergedC++] = array1[i];
i++;
}
while(j<arrLen2){
mergedArr[mergedC++] = array2[j];
j++;
}
return removeZero(mergedArr);
}
/**
* 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) {
// 最直接的做法,使用Arrays.copyOf()
// return Arrays.copyOf(oldArray, oldArray.length+size);
// 原始做法
int oldLen = oldArray.length;
int[] newArray = new int[oldLen + size];
for (int i = 0; i < oldLen; 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[]{};
} else {
int[] fibonacciArr = new int[100];
int growSize = 100;
fibonacciArr[0] = 1;
fibonacciArr[1] = 1;
int curFibNum;
int curIndex = 2;
while ((curFibNum = fibonacciArr[curIndex - 1] + fibonacciArr[curIndex - 2]) < max) {
if (curIndex == fibonacciArr.length) {
fibonacciArr = grow(fibonacciArr, growSize);
}
fibonacciArr[curIndex] = curFibNum;
curIndex++;
}
// 清理多余的0
return removeZero(fibonacciArr);
}
}
/**
* 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[] primesArr = new int[max];
// int growSize = 100;
int Count = 0;
for(int i=2;i<max;i++){
if(testIsPrime(i)){
primesArr[Count++] = i;
}
}
return removeZero(primesArr);
}
private boolean testIsPrime(int n){
if (n <= 3) {
return n > 1;
}
for(int i=2;i<=Math.sqrt(n);i++){
if(n%i == 0)
return false;
}
return true;
}
/**
* 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[] perfectArr = new int[max];
// int growSize = 100;
int Count = 0;
for(int i=2;i<max;i++){
if(isPerfectNum(i)){
perfectArr[Count++] = i;
}
}
return removeZero(perfectArr);
}
private boolean isPerfectNum(int inNum){
int sum = 1;
for(int i = 2;i<inNum;i++){
if(inNum%i==0){
sum+=i;
if(sum>inNum){
return false;
}
}
}
return sum == inNum;
}
/**
* 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) {
StringBuilder sb = new StringBuilder();
int loopMax = array.length-1;
for(int i=0;i<loopMax;i++){
sb.append(array[i]).append('-');
}
return sb.append(array[loopMax]).toString();
}
}