algorithm - Using Double Ended Queues (Deques) for Transposing sequences -


this interesting question might more interesting useful. want copy 2 deques(dq1_a , dq1_b) copies (dq2_a , dq2_b). 

dq1_a= <a,b,c,d,e,f> dq1_b= <g,h,i,j,k,l,m>

but want exchange "strands" @ d<->j. want end 

dq2_a= <a,b,c,(d or j),k,l,m> dq2_b= <g,h,i,(j or d),e,f>

the or exists because depends on whether include elements marking exchange in or not.

question 1: find algorithm end transposed datastructure dq2_* starting given deques dq1_* , exchanged elements ex=(d<->j); ex[a]=d; ex[b]=j. allowed deque operations - left_push,left_pop,right_push,right_pop,deque_empty(last 1 returns whether deque empty or not).

solution:

left_item  <- left_pop(dq1_a) while (left_item!=ex[a]):   right_push(dq2_a,left_item)   left_item<-left_pop(dq1_a)  right_item <- right_pop(dq1_b) while (right_item!=ex[b]):   left_push(dq2_b,right_item)   right_item<-right_pop(dq1_b)  # if not inclusive right_push(dq2_a,left_item) left_push(dq2_b,right_item) # else  #right_push(dq2_b,left_item) #left_push(dq2_a,right_item)  left_item  <- left_pop(dq1_b) while (not deque_empty(dq1_b)):   right_push(dq2_a,left_item)   left_item<-left_pop(dq1_a)  right_item <- right_pop(dq1_a) while (not deque_empty(dq1_a)):   left_push(dq2_b,right_item)   right_item<-rightt_pop(dq1_a)

question 2: beats me. given set of dq1_* (more 2) - have copy them dq2_* using list of exchanges 

ex={s: s given set of exchanges of form: (ith element of dq1_x)<->(jth element of dq1_y)}

any better solutions problem welcome!!


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