Doubly-linked list/Element removal: Difference between revisions
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Then deleting node2 yields: |
Then deleting node2 yields: |
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1 -> 4 |
1 -> 4 |
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</pre> |
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=={{header|Phix}}== |
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Extended copy of [[Doubly-linked_list/Traversal#Phix]] |
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<lang Phix>enum NEXT,PREV,DATA |
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constant empty_dll = {{1,1}} |
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sequence dll = empty_dll |
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procedure remove_item(integer pos) |
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if pos<=1 or pos>length(dll) then ?9/0 end if -- (sanity check) |
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integer {next,prev} = dll[pos] |
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dll[prev][NEXT] = next |
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dll[next][PREV] = prev |
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if pos<length(dll) then |
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dll[pos] = dll[$] |
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{next,prev} = dll[pos] |
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dll[prev][NEXT] = pos |
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dll[next][PREV] = pos |
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end if |
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dll = dll[1..-2] |
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end procedure |
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procedure insert_after(object data, integer pos=1) |
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integer prv = dll[pos][PREV] |
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dll = append(dll,{pos,prv,data}) |
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if prv!=0 then |
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dll[prv][NEXT] = length(dll) |
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end if |
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dll[pos][PREV] = length(dll) |
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end procedure |
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insert_after("ONE") |
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insert_after("TWO") |
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insert_after("THREE") |
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?dll |
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procedure show(integer d) |
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integer idx = dll[1][d] |
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while idx!=1 do |
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?dll[idx][DATA] |
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idx = dll[idx][d] |
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end while |
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end procedure |
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show(NEXT) |
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?"==" |
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show(PREV) |
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while length(dll)>1 do |
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?"== removing one item ==" |
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remove_item(rand(length(dll)-1)+1) |
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show(NEXT) |
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?"==" |
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show(PREV) |
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end while</lang> |
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{{out}} |
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<pre> |
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{{2,4},{3,1,"ONE"},{4,2,"TWO"},{1,3,"THREE"}} |
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"ONE" |
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"TWO" |
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"THREE" |
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"==" |
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"THREE" |
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"TWO" |
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"ONE" |
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"== removing one item ==" |
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"ONE" |
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"THREE" |
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"==" |
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"THREE" |
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"ONE" |
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"== removing one item ==" |
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"THREE" |
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"==" |
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"THREE" |
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"== removing one item ==" |
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"==" |
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</pre> |
</pre> |
Revision as of 18:05, 28 September 2020
- Task
Define a method to remove an element from a doubly-linked list and demonstrate its use.
You may wish to use the list element defined in Doubly-Linked List (element) for the purposes of this task.
ALGOL W
Uses the element type and insertion method as in the Doubly-Linked List (traversal) task. <lang algolw>begin
% record type to hold an element of a doubly linked list of integers % record DListIElement ( reference(DListIElement) prev ; integer iValue ; reference(DListIElement) next ); % additional record types would be required for other element types % % inserts a new element into the list, before e % reference(DListIElement) procedure insertIntoDListIBefore( reference(DListIElement) value e ; integer value v ); begin reference(DListIElement) newElement; newElement := DListIElement( null, v, e ); if e not = null then begin % the element we are inserting before is not null % reference(DListIElement) ePrev; ePrev := prev(e); prev(newElement) := ePrev; prev(e) := newElement; if ePrev not = null then next(ePrev) := newElement end if_e_ne_null ; newElement end insertIntoDListiAfter ; % removes an element e of a doubly linked list % procedure removeDListIElement( reference(DListIElement) value e ); if e not = null then begin % have an element to remove % reference(DListIElement) ePrev, eNext; ePrev := prev(e); eNext := next(e); if ePrev not = null then next(ePrev) := eNext; if eNext not = null then prev(eNext) := ePrev end removeDListIElement ;
begin reference(DListIElement) head, e, toRemove, last; head := null; head := insertIntoDListIBefore( head, 1701 ); head := insertIntoDListIBefore( head, 9000 ); e := insertIntoDListIBefore( next(head), 90210 ); toRemove := insertIntoDListIBefore( next(e), 4077 ); e := head; last := null; write( "Before: Forward:" ); while e not = null do begin write( i_w := 1, s_w := 0, " ", iValue(e) ); last := e; e := next(e) end while_e_ne_null ; write( "Before: Backward:" ); e := last; while e not = null do begin write( i_w := 1, s_w := 0, " ", iValue(e) ); last := e; e := prev(e) end while_e_ne_null ; e := head; last := null;
% remove an element % removeDListIElement( toRemove );
write( "After: Forward:" ); while e not = null do begin write( i_w := 1, s_w := 0, " ", iValue(e) ); last := e; e := next(e) end while_e_ne_null ; write( "After: Backward:" ); e := last; while e not = null do begin write( i_w := 1, s_w := 0, " ", iValue(e) ); last := e; e := prev(e) end while_e_ne_null end
end.</lang>
- Output:
Before: Forward: 9000 90210 4077 1701 Before: Backward: 1701 4077 90210 9000 After: Forward: 9000 90210 1701 After: Backward: 1701 90210 9000
Julia
Uses code from Doubly-Linked List (traversal) <lang julia>mutable struct DLNode{T}
value::T pred::Union{DLNode{T}, Nothing} succ::Union{DLNode{T}, Nothing} DLNode(v) = new{typeof(v)}(v, nothing, nothing)
end
function insertpost(prevnode, node)
succ = prevnode.succ prevnode.succ = node node.pred = prevnode node.succ = succ if succ != nothing succ.pred = node end return node
end
function delete(node)
succ = node.succ pred = node.pred succ != nothing && (succ.pred = pred) pred != nothing && (pred.succ = succ) return node
end
first(nd) = (while nd.pred != nothing nd = nd.prev end; nd) last(nd) = (while nd.succ != nothing nd = nd.succ end; nd)
function atindex(nd, idx)
nd = first(nd) while idx > 1 && nd != nothing nd = nd.succ idx -= 1 end return nd
end
function printconnected(nd; fromtail = false)
if fromtail nd = last(nd) print(nd.value) while nd.pred != nothing nd = nd.pred print(" -> $(nd.value)") end else nd = first(nd) print(nd.value) while nd.succ != nothing nd = nd.succ print(" -> $(nd.value)") end end println()
end
node1 = DLNode(1) node2 = DLNode(2) node3 = DLNode(3) node4 = DLNode(4)
insertpost(node1, node2) insertpost(node2, node3) insertpost(node3, node4)
print("From beginning to end: "); printconnected(node1) delete(atindex(node1, 3)) println("Deleting third node yields: "); printconnected(node1) delete(node2) println("Then deleting node2 yields: "); printconnected(node1)
</lang>
- Output:
From beginning to end: 1 -> 2 -> 3 -> 4 Deleting third node yields: 1 -> 2 -> 4 Then deleting node2 yields: 1 -> 4
Phix
Extended copy of Doubly-linked_list/Traversal#Phix <lang Phix>enum NEXT,PREV,DATA constant empty_dll = Template:1,1 sequence dll = empty_dll
procedure remove_item(integer pos)
if pos<=1 or pos>length(dll) then ?9/0 end if -- (sanity check) integer {next,prev} = dll[pos] dll[prev][NEXT] = next dll[next][PREV] = prev if pos<length(dll) then dll[pos] = dll[$] {next,prev} = dll[pos] dll[prev][NEXT] = pos dll[next][PREV] = pos end if dll = dll[1..-2]
end procedure
procedure insert_after(object data, integer pos=1) integer prv = dll[pos][PREV]
dll = append(dll,{pos,prv,data}) if prv!=0 then dll[prv][NEXT] = length(dll) end if dll[pos][PREV] = length(dll)
end procedure
insert_after("ONE") insert_after("TWO") insert_after("THREE")
?dll
procedure show(integer d) integer idx = dll[1][d]
while idx!=1 do ?dll[idx][DATA] idx = dll[idx][d] end while
end procedure show(NEXT) ?"==" show(PREV) while length(dll)>1 do
?"== removing one item ==" remove_item(rand(length(dll)-1)+1) show(NEXT) ?"==" show(PREV)
end while</lang>
- Output:
{{2,4},{3,1,"ONE"},{4,2,"TWO"},{1,3,"THREE"}} "ONE" "TWO" "THREE" "==" "THREE" "TWO" "ONE" "== removing one item ==" "ONE" "THREE" "==" "THREE" "ONE" "== removing one item ==" "THREE" "==" "THREE" "== removing one item ==" "=="