我一直在练习算法，递归总是我的弱点。此问题要求将嵌套数组展平为单个数组。如果使用一个给出O（n ^ 3）[给定一个大小相同的3d数组]解决方案的循环，这将很简单。
然而，随着递归，我一直在努力奋斗几个小时。这就是我所拥有的，请注意我已经尝试了我的代码尝试不同的解决方案，这就是我决定留下来发布给你们的人。
我想要的是两件事，无论如何要修复我当前的代码以获得正确的输出，并且使用递归编写此代码的方法更简单，更简洁！谢谢！
奖金问题，如果我不知道嵌套数组的维度，那么我如何使用递归来解决这个问题呢？
修改 好吧，经过一些硬编码（我不想做），我设法让这个工作。但是代码现在是硬编码而且非常混乱，无论如何都要清理代码或者使用递归来解决这个问题的简单方法？
EDIT2 我正在尝试使用辅助方法递归重做此问题。我会看看我是否有更好的运气使用这种风格
import java.io. * ;
import java.util. * ;
class Solution {
// static int oneLen = 0;
//static int twoLen = 0;
//static int threeLen = 0;
static int oneCnt = 0;
static int twoCnt = 0;
static int threeCnt = 0;
static ArrayList < Integer > result = new ArrayList < Integer > ();
public static ArrayList < Integer > flatten(int [][][] arr){
if (oneCnt < arr[threeCnt][twoCnt].length && !(oneCnt == 2 && twoCnt == 2 && threeCnt == 2))
{
if (oneCnt == 0 && twoCnt == 0 && threeCnt == 0){
result.add(arr[threeCnt][twoCnt][oneCnt]);
oneCnt++;
result.add(arr[threeCnt][twoCnt][oneCnt]);
System.out.println("Line One");
System.out.println("Count1: " + oneCnt);
System.out.println("Count2: " + twoCnt);
System.out.println("Count3: " + threeCnt);
}
oneCnt++;
if (oneCnt != 3){
result.add(arr[threeCnt][twoCnt][oneCnt]); }
System.out.println("Line One");
System.out.println("Count1: " + oneCnt);
System.out.println("Count2: " + twoCnt);
System.out.println("Count3: " + threeCnt);
flatten(arr);
} else if (oneCnt == arr[threeCnt][twoCnt].length && twoCnt < arr[threeCnt].length - 1){
//oneLen = 0;
oneCnt = 0;
// twoLen++;
twoCnt++;
result.add(arr[threeCnt][twoCnt][oneCnt]);
System.out.println("Line Two");
System.out.println("Count:1 " + oneCnt);
System.out.println("Count:2 " + twoCnt);
System.out.println("Count:3 " + threeCnt);
flatten(arr);
}
else if (oneCnt == arr[threeCnt][twoCnt].length && twoCnt == arr[threeCnt].length - 1 && threeCnt < arr.length - 1){
oneCnt = 0;
twoCnt = 0;
threeCnt++;
result.add(arr[threeCnt][twoCnt][oneCnt]);
System.out.println("Line Three");
System.out.println("Count:1 " + oneCnt);
System.out.println("Count:2 " + twoCnt);
System.out.println("Count:3 " + threeCnt);
flatten(arr);
}
return result;
}
public static void main(String[] args) {
int[][][] array =
{ { {1, 2, 3}, { 4, 5, 6}, { 7, 8, 9} },
{ {10, 11, 12}, {13, 14, 15}, {16, 17, 18} },
{ {19, 20, 21}, {22, 23, 24}, {25, 26, 27} } };
flatten(array);
for (int i = 0; i < result.size(); i++){
System.out.print(result.get(i) + ",");
}
}
}
输出：1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23 ，24,25,26,27，
EDIT3 使用帮助器递归后，我几乎得到了答案，但最后一个元素不会添加到arraylist。
import java.io. * ;
import java.util. * ;
class Solution {
static ArrayList < Integer > result = new ArrayList < Integer > ();
public static void flatten(int [][][] arr){
int oneLen = 0;
int twoLen = 0;
int threeLen = 0;
flattenHelper(arr, oneLen, twoLen, threeLen);
}
public static void flattenHelper(int [][][] arr, int oneLen, int twoLen, int threeLen){
if (oneLen < arr[threeLen][twoLen].length - 1){
System.out.println("Line One");
System.out.println("Count:1 " + oneLen);
System.out.println("Count:2 " + twoLen);
System.out.println("Count:3 " + threeLen);
result.add(arr[threeLen][twoLen][oneLen]);
flattenHelper(arr, oneLen + 1, twoLen, threeLen);
}
else if (twoLen < arr[threeLen].length - 1){
System.out.println("Line Two");
System.out.println("Count:1 " + oneLen);
System.out.println("Count:2 " + twoLen);
System.out.println("Count:3 " + threeLen);
result.add(arr[threeLen][twoLen][oneLen]);
flattenHelper(arr, oneLen = 0, twoLen + 1, threeLen);
} else if (threeLen < arr.length - 1){
System.out.println("Line Two");
System.out.println("Count:1 " + oneLen);
System.out.println("Count:2 " + twoLen);
System.out.println("Count:3 " + threeLen);
result.add(arr[threeLen][twoLen][oneLen]);
flattenHelper(arr, oneLen = 0, twoLen = 0, threeLen + 1);
}
}
public static void main(String[] args) {
int[][][] array =
{ { {1, 2, 3}, { 4, 5, 6}, { 7, 8, 9} },
{ {10, 11, 12}, {13, 14, 15}, {16, 17, 18} },
{ {19, 20, 21}, {22, 23, 24}, {25, 26, 27} } };
flatten(array);
for (int i = 0; i < result.size(); i++){
System.out.print(result.get(i) + ",");
}
}
}
输出：1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23 ，24,25,26，
答案 0 :(得分：5)
它是递归的，您不需要更改输入结构，也不需要知道数组的维度。你可以疯狂并混合Arrays，Lists和其他对象，它将返回一个ArrayList：
package stackOverflow;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.List;
public class Solution
{
public static void main(String[] args) {
int[][][] int3dArray = { { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } },
{ { 10, 11, 12 }, { 13, 14, 15 }, { 16, 17, 18 } },
{ { 19, 20, 21 }, { 22, 23, 24 }, { 25, 26, 27 }, { 28 }, { 29, 30 } } };
String[][] string2dArray = { { "He, llo" }, { "Wo", "rld" } };
String[] stringArray = { "Hello", "World" };
Object[] objectArray = { "Hell", 0, "W", 0, "rld" };
List<Object> mixList = new ArrayList<Object>();
mixList.add("String");
mixList.add(3);
mixList.add(string2dArray);
System.out.println(flatten(int3dArray));
System.out.println(flatten(flatten(int3dArray)));
System.out.println(flatten(3));
System.out.println(flatten(stringArray));
System.out.println(flatten(string2dArray));
System.out.println(flatten(objectArray));
System.out.println(flatten(mixList));
}
private static List<Object> flatten(Object object) {
List<Object> l = new ArrayList<Object>();
if (object.getClass().isArray()) {
for (int i = 0; i < Array.getLength(object); i++) {
l.addAll(flatten(Array.get(object, i)));
}
} else if (object instanceof List) {
for (Object element : (List<?>) object) {
l.addAll(flatten(element));
}
} else {
l.add(object);
}
return l;
}
}
输出：
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30]
[3]
[Hello, World]
[He, llo, Wo, rld]
[Hell, 0, W, 0, rld]
[String, 3, He, llo, Wo, rld]
这是一个modified version，它还将地图展平为一组值。它可以输出Set或List。
这是我的原始解决方案，它只显示结果，但返回void：
package stackOverflow;
import java.lang.reflect.Array;
public class Solution
{
public static void main(String[] args) {
int[][][] array = { { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } },
{ { 10, 11, 12 }, { 13, 14, 15 }, { 16, 17, 18 } },
{ { 19, 20, 21 }, { 22, 23, 24 }, { 25, 26, 27 }, { 28 } } };
flatten(array);
}
private static void flatten(Object object) {
if (object.getClass().isArray()) {
for (int i = 0; i < Array.getLength(object); i++) {
flatten(Array.get(object, i));
}
} else {
System.out.print(object + ",");
}
}
}
它返回： 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25， 26,27,28，
答案 1 :(得分：1)
如果您可以将数据更改为Integer数组而不是int，您可以检查传递的数组的元素并递归数组元素，或者只是直接将它们添加到结果中。
public static ArrayList<Integer> flatten(Object [] arr) {
ArrayList<Integer> result = new ArrayList<>();
for (int i = 0; i < arr.length; i++) {
if (arr[i].getClass().isArray()){
result.addAll(flatten((Object[])arr[i]));
} else {
result.add((int)arr[i]);
}
}
return result;
}