MERGE.A; p; q; r$/$

$1$ nL D q $$ p C $1//$ length of A$$p W q$$

$2$ nR D r $$ q $//$ length of A$$q C $1$ W r$$

$3$ let L$0$ W nL $1$ and R$0$ W nR $1$ be new arrays

$4$ for i D $0$ to nL $1//$ copy A$$p W q$$ into L$0$ W nL $1$

$5$ L$$i$$ D A$$p C i$$

$6$ for j D $0$ to nR $1//$ copy A$$q C $1$ W r$$ into R$0$ W nR $1$

$7$ R$$j $$ D A$$q C j C $1$

$8$ i D $0//$ i indexes the smallest remaining element in L

$9$ j D $0//$ j indexes the smallest remaining element in R

$10$ k D p $//$ k indexes the location in A to $$ll

$11//$ As long as each of the arrays L and R contains an unmerged element,

$//$ copy the smallest unmerged element back into A$$p W r$.$

$12$ while i $<$ nL and j $<$ nR

$13$ if L$$i$$ R$$j $$

$14$ A$$k$$ D L$$i$$

$15$ i D i C $1$

$16$ else A$$k$$ D R$$j $$

$17$ j D j C $1$

$18$ k D k C $1$

$19//$ Having gone through one of L and R entirely, copy the

$//$ remainder of the other to the end of A$$p W r$.$

$20$ while i $<$ nL

$21$ A$$k$$ D L$$i$$

$22$ i D i C $1$

$23$ k D k C $1$

$24$ while j $<$ nR

$25$ A$$k$$ D R$$j $$

$26$ j D j C $1$

$27$ k D k C $1$