How can I find duplicate integers between two arrays and copy them into a new array?

user_17602620 0
Viewed 116

To begin, I am doing this using only arrays (no hash maps or array lists).

I am trying to create a method, project, which inputs two integer arrays with different sizes.

I am trying to compare them in a way to get the following output: projecting [1, 3, 5, 3] to [2, 1, 6, 3, 1, 4, 5, 3] results in: [1, 3, 1, 5, 3]. However, projecting [2, 1, 6, 3, 1, 4, 5, 3] to [1, 3, 5, 3] results in: [1, 3, 5, 3].

I believe the nested for loop might be wrong as it is iterating through the first indices for the first array all the way through the second array, then going to the next.

I'm getting an ArrayIndexOutOfBoundsException for the starred line (tempArray[i] == arr1[i], I know it shouldn't be tempArray[i] but not sure what exactly to put).

I'm not sure how to compare them in a way to produce the line above, as it needs to be "in order". What could be the best way to accomplish this?

I attempted the following code:

public int[] project(int[] arr1, int[] arr2) {
    int counter = 0;
    for (int i = 0; i < arr1.length; i++) {
        for (int j = 0; j < arr2.length; j++) {
            if (arr1[i] == arr2[j]) {
                counter++;
            }
        }
    }
    
    int[] tempArray = new int[counter];
    for(int i = 0 ; i < arr1.length; i++) {
        for (int j = 0; j < arr2.length; j++) {
            if(arr1[i] == arr2[j]) {
                tempArray[i] = arr1[i]; // UNDERLINED
            }
        }
    }
}

Edit

The ArrayIndexOutOfBounds error is gone, but now my return statement is: projecting [1, 3, 5] to [2, 1, 6, 3, 1, 4, 5, 3] results in: [1, 3, 5, 0, 0], when it needs to be: projecting [1, 3, 5] to [2, 1, 6, 3, 1, 4, 5, 3] results in: [1, 3, 1, 5, 3].

Any idea what is causing this issue?

computer-science arrays java
5 Answers

I think you have a typo in your first for loop

change this to later

arr1[i] == arr2[i]

to

arr1[i] == arr2[j]

Regarding overlapping issues in the projection array, you need to maintain different value as your index rather than i or j which is used by arr1 and arr2 respectively

int[] tempArray = new int[counter];
int index = 0;

for(int i=0 ; i < arr1.length; i++) {
    for (int j=0; j < arr2.length; j++) {
        if(arr1[i] == arr2[j]) {
            tempArray[index++] = arr1[i];
        }
    }
}

For the values which you are expecting you should loop through arr2 first

for(int j=0 ; j < arr2.length; j++) {
    for (int i=0; i < arr1.length; i++) {
        if(arr1[i] == arr2[j]) {
            tempArray[index++] = arr1[i];
        }
    }
}

If the contents of array are not hardcoded and you dont know the order in which you want to pass, you can make use of length

  int[] ans;
  if(a.length < b.length) {
      ans = project(a, b);
  } else {
      ans = project(b, a);
  }

Output:

[1, 3, 1, 5, 3]

user_92769960

You currently have index variables (i, j) tracking the indexes of each input array as you loop through them, but you also need to keep track of the write head of the result array. Initialize, say int k = 0 before the outer for loop, then set the value like this: tempArray[k++] = array1[i];.

You can forgo the first loop If you are OK with performing a single array copy. Initialize an array as long as the second input array (since there can never be more duplicated elements than existing elements) as the tempArray. Then if you want it to fit exactly, initialize the final array to the exact length k and use System#arrayCopy.

user_33633860

this will probably solve your problem

public int[] project(int[] arr1, int[] arr2) {
    int counter = 0;
    for (int i : arr2) {
        if (Arrays.binarySearch(arr1, i) >= 0) {
            counter++;
        }
    }
    int[] arr4 = new int[counter];
    int index = 0;
    for (int i : arr2) {
        if (Arrays.binarySearch(arr1, i) >= 0) {
            arr4[index++] = i;
        }
    }

    return arr4;
}
user_92368520

The nested iteration is expensive, so we want to avoid that. The first thing to do is sort the array we are projecting from so we can perform a binary search on it. Second, don't execute the nested iteration to determine the output array size. Create an array the size of the array we are projecting to since it can be no longer than that.

public int[] projection(int[] a, int[] b) {
  int[] temp = new int[b.length];
  int nextIndex = 0;
  for (int x : b) {
    if (contains(a, x)) {
      temp[nextIndex++] = x;
    }
  }
  return slice(temp, nextIndex);
}

private boolean contains(int[] array, int value) {
  for (int element : array) {
    if (element == value) {
      return true;
    }
  }
  return false;
}

private int[] slice(int[] src, int size) {
  int[] slice = new int[size];
  for (int index = 0 ; index < size ; ++index) {
    slice[index] = src[index];
  }
  return slice;
}
user_72750560

For your second problem, I think, in your temporary array, you should be saving the values from arr2[j] instead of arr1[i].

Also, you need a different counter (set to 0 initially and incremented in the loop) for setting the values in tempArray[counter].

What I mean exactly is:

int counter = 0;
for (int i = 0; i < arr1.length; i++) {
    for (int j = 0; j < arr2.length; j++) {
        if (arr1[i] == arr2[j]) {
            tempArray[counter] = arr2[j];
            counter++;           
        }
    }
}
user_85239910
Related