So the goal of this code is to recursively move through a 2d array with frogs on certain cells. A frog can jump over another frog and delete it. This code is supposed to see how many different ways you can do that to get it to one frog. But after one path is found, the original array is changed and it still only has a single frog from the previous path. How do I change this so that the original array isn’t affected?
public void RecursiveFunc(Units[][] array) {
for(int x = 0; x < array.length; x++){
for(int y = 0; y < array.length; y++) {
temp[x][y] = array[x][y];
}
}
//make move on temp board and recursively call again
if (CheckNumberFrogs(temp) == 1 && CheckLastID(temp) == getgoalLoc()) {
numOfPlans += 1;
}
else {
for(int i= 0; i < temp.length; i++){
for(int j = 0; j < temp.length; j++){
if (temp[i][j].Frog == true) {
//Every possible movement is done here and then recursively recalled
if (i > 1) {
//can go left
if (temp[i-1][j].Frog == true && temp[i-2][j].Frog == false) {
temp[i][j].removeFrog();
temp[i-1][j].removeFrog();
temp[i-2][j].setFrog();
RecursiveFunc(temp);
for(int x = 0; x < array.length; x++){
for(int y = 0; y < array.length; y++) {
temp[x][y] = array[x][y];
}
}
}
}
if (i < (temp.length - 2)) {
//can go right
if (temp[i+1][j].Frog == true && temp[i+2][j].Frog == false) {
temp[i][j].removeFrog();
temp[i+1][j].removeFrog();
temp[i+2][j].setFrog();
RecursiveFunc(temp);
for(int x = 0; x < array.length; x++){
for(int y = 0; y < array.length; y++) {
temp[x][y] = array[x][y];
}
}
}
}
if (j > 1) {
//can go down
if (temp[i][j-1].Frog == true && temp[i][j-2].Frog == false) {
temp[i][j].removeFrog();
temp[i][j-1].removeFrog();
temp[i][j-2].setFrog();
RecursiveFunc(temp);
for(int x = 0; x < array.length; x++){
for(int y = 0; y < array.length; y++) {
temp[x][y] = array[x][y];
}
}
}
}
if(j < (temp.length - 2)) {
//can go up
if (temp[i][j+1].Frog == true && temp[i][j+2].Frog == false) {
temp[i][j].removeFrog();
temp[i][j+1].removeFrog();
temp[i][j+2].setFrog();
RecursiveFunc(temp);
for(int x = 0; x < array.length; x++){
for(int y = 0; y < array.length; y++) {
temp[x][y] = array[x][y];
}
}
}
}
if (i > 1 && j > 1) {
//can go left and down (diagonal)
if (temp[i-1][j-1].Frog == true && temp[i-2][j-2].Frog == false) {
temp[i][j].removeFrog();
temp[i-1][j-1].removeFrog();
temp[i-2][j-2].setFrog();
RecursiveFunc(temp);
for(int x = 0; x < array.length; x++){
for(int y = 0; y < array.length; y++) {
temp[x][y] = array[x][y];
}
}
}
}
if (i < (temp.length - 2) && j > 1) {
//can go right and down (diagonal)
if (temp[i+1][j-1].Frog == true && temp[i+2][j-2].Frog == false) {
temp[i][j].removeFrog();
temp[i+1][j-1].removeFrog();
temp[i+2][j-2].setFrog();
RecursiveFunc(temp);
for(int x = 0; x < array.length; x++){
for(int y = 0; y < array.length; y++) {
temp[x][y] = array[x][y];
}
}
}
}
if (i > 1 && j < (temp.length - 2)) {
//can go left and up (diagonal)
if (temp[i-1][j+1].Frog == true && temp[i-2][j+2].Frog == false) {
temp[i][j].removeFrog();
temp[i-1][j+1].removeFrog();
temp[i-2][j+2].setFrog();
RecursiveFunc(temp);
for(int x = 0; x < array.length; x++){
for(int y = 0; y < array.length; y++) {
temp[x][y] = array[x][y];
}
}
}
}
if (i < (temp.length - 2) && j < (temp.length - 2)) {
//can go right and up (diagonal)
if (temp[i+1][j+1].Frog == true && temp[i+2][j+2].Frog == false) {
temp[i][j].removeFrog();
temp[i+1][j+1].removeFrog();
temp[i+2][j+2].setFrog();
RecursiveFunc(temp);
for(int x = 0; x < array.length; x++){
for(int y = 0; y < array.length; y++) {
temp[x][y] = array[x][y];
}
}
}
}
//end
}
}
}
}
}
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Answer
You have to explicitly make a copy of the array and store it.
For a two-dimensional array, this means you need an entire loop to copy the array:
int[][] copy(int[][] array) {
int[][] result = new int[array.length][];
for (int i = 0; i < array.length; i++) {
result[i] = Arrays.copyOf(array[i], array[i].length);
}
return result;
}
As for why, remember that objects are arrays and study https://stackoverflow.com/a/40523/869736.