I'm trying to merge two sorted arrays but getting java.lang.ArrayIndexOutOfBoundsException: 5 can't figure out why

Question

It is going out bounds on the first if statement even after I'm checking the values of j and k before incrementing

`int[] Merge(int[]a,int[]b){
int n=a.length+b.length;
int[] sol= new int[n];
int i=0,j=0,k=0;

while(i<n){

if(a[j]<b[k]){

    sol[i]=a[j];

    if(j<a.length)j++;
}
else if(b[k]<a[j]){

        sol[i]=b[k];

        if(k<b.length)k++;

}

i++;

}


return sol;

}`

I can't understand where the array is going out of bounds

Answer 1

Consider the case when either j=a.length-1 or k=b.length-1 then your if condition [ if(j<a.length)j++ ; or if(k<b.length)k++; ]passes and makes j==a.length to true or k==b.length to true and the while loop access the array again when it throws ArrayIndexOutofBound exception. Also your code doesn't handle common elements in the array. Please check the correct code below

int[] Merge(int[]a,int[]b){
int n=a.length+b.length;
        int[] sol= new int[n];
        int i=0,j=0,k=0;

        while(i<n){
            if(a[j]<=b[k]){ // equality check handles common case

                sol[i++]=a[j++];
                if(j==a.length)
                   break;

            }
            else if(b[k]<a[j]){
                sol[i++]=b[k++];
                if(k==b.length)
                    break ;

            }


        }
        if(j==a.length) {
            while (k != b.length)
                sol[i++]=b[k++];
        }
        if(k==b.length) {
            while (j != a.length)
                sol[i++]=a[j++];
        }
        return sol;
}

Answer 2

The problem is here:

if(j<a.length)j++;

Here when j = a.length - 1 then it will become a.length because of j++. Now, a[j] will be out of bounds because j = a.length. a[a.length] is always out bounds. The indexing starts from 0, so last index is a.length - 1.