1. The Potential Method

2. Deque with stacks size=7 13 S1S1 S2S2 push(x,D): push(x,S 1 ) 5 4 17 21 8 7 push(2,D)

3. Implementation with stacks size=8 2 13 S1S1 S2S2 push(x,D): push(x,S 1 ) 5 4 17 21 8 7 push(2,D)

4. Pop size=8 S1S1 S2S2 pop(D): if empty?(D) error if empty?(S 1 ) then split(S 2, S 1 ) pop( S 1 ) 2 13 5 4 17 21 8 7 pop(D)

5. Pop size=7 S1S1 S2S2 pop(D): if empty?(D) error if empty?(S 1 ) then split(S 2, S 1 ) pop( S 1 ) 13 5 4 17 21 8 7 pop(D) pop(D)

6. Pop size=6 S1S1 S2S2 pop(D): if empty?(D) error if empty?(S 1 ) then split(S 2, S 1 ) pop( S 1 ) 5 4 17 21 8 7 pop(D) pop(D)

7. Pop 17 21 8 7 size=6 S1S1 S2S2 pop(D): if empty?(D) error if empty?(S 1 ) then split(S 2, S 1 ) pop( S 1 ) pop(D) 5 4

8. Delete from Queue 17 21 8 7 size=5 S1S1 S2S2 4 Pop 17 21 8 size=4 S1S1 S2S2 4

9. The potential method

11. If then.

12. PUSH The same for POP without split

13. 5 4 17 21 8 7 S1S1 S2S2 17 21 8 7 S1S1 S2S2 5 4 s=6 s/32s/3 POP that calls SPLIT