将两个排序数组排序为新排序数组的最有效方法

Question

I am trying to sort two int arrays into a new int array in ascending order.

I wrote it like this and it sorted everything but the last element in textArr and I couldn't figure out why...

int i=0, j=0, k=0;
while(i < textArr.length && j < binaryArr.length) {
    if(textArr[i] < binaryArr[j]) {
        mergeArr[k] = textArr[i];
        i++;
    }
    else {
        mergeArr[k] = binaryArr[j];
        j++;
    }
    k++;
}

I looked around and found a solution that added two new while loops but I honestly do not know what those second two while loops are doing. I'd also like to know if this is the most efficient way to sort two arrays into a third sorted array? Thanks for any help, I'm very new to java and would like to learn correctly and obviously I want to learn what I'm actually writing too!

int i=0, j=0, k=0;
while(i < textArr.length && j < binaryArr.length) {
    if(textArr[i] < binaryArr[j]) {
        mergeArr[k] = textArr[i];
        i++;
    }
    else {
        mergeArr[k] = binaryArr[j];
        j++;
    }
    k++;
}
while(i < textArr.length) {
    mergeArr[k] = textArr[i];
    i++;
    k++;
}       

Answer 1

Here is your code with comments explaining why the final two loops are required.

int[] textArr = {1, 2, 3, 3, 9};
int[] binaryArr = {4, 5, 6};
int[] mergeArr = new int[textArr.length + binaryArr.length];

int i=0, j=0, k=0;
while(i < textArr.length && j < binaryArr.length) {
    if(textArr[i] < binaryArr[j]) {
        mergeArr[k] = textArr[i];
        i++;
    }
    else {
        mergeArr[k] = binaryArr[j];
        j++;
    }
    k++;
}
// At this point either i == textArr.length or j == binaryArr.length
// so you cannot do textArr[i] < binaryArr[j] without getting
// an ArrayIndexOutOfBoundsException. 
// However the algorithm isn't finished. You still need to transfer
// the remaining numbers from one of the original arrays into the answer.
while(i < textArr.length) {
    mergeArr[k] = textArr[i];
    i++;
    k++;
}
while(j < binaryArr.length) {   // It said i in question. I corrected.
    mergeArr[k] = binaryArr[j];
    k++;
    j++;
}

System.out.println(Arrays.toString(mergeArr));

As for whether this is the most efficient code. It's about as good as you can get. Any algorithm has to read all the numbers so you can't do better than O(n + m) where n and m are the lengths of the original arrays. You could slightly improve performance by replacing the final while loops with System.arraycopy .

Answer 2

Basic algorithm for merging two sorted arrays of size n . This should be enough to go off of for the more generic "merge two sorted arrays of size m and n respectively"

//given arrays A, B, create C
var i, j = 0, k = 0;
for (i = 0; i < 2n; i++) {
  if (A[j] < B[k]) { 
    C[i] = A[j++]; 
  }
  else { 
    C[i] = B[k++];
  }
}