package com.coderising.array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedList;
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){
if(origin == null) return;
int tmp;
for(int i = 0; i< origin.length; i++){
int end = origin.length - 1 -i;
if(end>i){
tmp = origin[i];
origin[i] = origin[end];
origin[end] = tmp;
}
}
}
/**
* 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){
LinkedList<Integer> newArray = new LinkedList<>();
for(int i = 0; i< oldArray.length; i++){
if(oldArray[i] != 0){
newArray.add(oldArray[i]);
}
}
int[] ret = new int[newArray.size()];
for(int i = 0; i<newArray.size(); i++){
ret[i] = newArray.get(i);
}
return ret;
}
/**
* 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.length == 0) return array2;
if(array2.length == 0) return array1;
int i = 0, j=0, index=0;
int[] merged = new int[array1.length + array2.length];
//o(n+m)
while(i < array1.length && j < array2.length){
if(array1[i] < array2[j]){
merged[index] = array1[i];
i++;
}else if(array1[i] >= array2[j]){
merged[index] = array2[j];
j++;}
// }else{
// merged[index] = array1[i];
// i++;
// j++;
// }
index++;
}
//o(n)
while(i<array1.length){
merged[index] = array1[i];
i++;
index++;
}
//o(m)
while(j<array2.length){
merged[index] = array1[j];
j++;
index++;
}
//o(n+m)
int low=0, high = 1; ;
while(high < merged.length){
if(merged[high] != merged[low]){
low++;
merged[low] = merged[high];
}
high ++;
}
return Arrays.copyOf(merged, low+1);
}
/**
* 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[] newArray = new int[oldArray.length + size];
System.arraycopy(oldArray, 0, newArray, 0, oldArray.length);
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[0];
int[] memo = new int[max+2];
int n = 1;
while(fib(n, memo)<max){
n++;
}
//System.out.println(Arrays.toString(memo));
int[] ret = new int[n-1];
System.arraycopy(memo, 1, ret, 0, n-1);
//System.out.println(Arrays.toString(ret));
return ret;
}
private int fib(int n, int[] memo){
if(n <= 0) return 0;
if(n == 1) {
if(memo[1] == 0){
memo[1] = 1;
}
return 1;
}
else{
if(memo[n] == 0){
memo[n] = fib(n-1, memo) + fib(n-2, memo);
}
return memo[n];
}
}
/**
* 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[] ret = new int[max];
int count =0;
for(int i = 1; i<= max; i++){
if(isPrime(i)){
ret[count++] = i;
}
}
return Arrays.copyOf(ret, count);
}
private boolean isPrime(int n){
for(int i = 2; i*i <=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){
if(max <2) return new int[0];
List<Integer> store = new LinkedList<>();
for(int candidate = 2; candidate< max; candidate++ ){
int sum = 0;
for(int i = 1; i<candidate; i++){
if(candidate%i == 0){
sum+=i;
}
}
if(sum == candidate){
store.add(sum);
}
}
int[] ret = new int[store.size()];
int index = 0;
for(Integer num : store){
ret[index++] = num.intValue();
}
return ret;
}
/**
* 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 lo = 0; lo<array.length; lo++){
sb.append(array[lo]);
if(lo < array.length -1)
sb.append(seperator);
}
return sb.toString();
}
}