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September 2017 Update

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Ingy döt Net 2017-09-23 10:01:46 +02:00
parent bba7bfd280
commit ba8067c3b7
14570 changed files with 153136 additions and 63871 deletions
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Task/Quickselect-algorithm/ALGOL-68/quickselect-algorithm.alg Normal file
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BEGIN
# returns the kth lowest element of list using the quick select algorithm #
PRIO QSELECT = 1;
OP QSELECT = ( INT k, REF[]INT list )INT:
IF LWB list > UPB list THEN
# empty list #
0
ELSE
# non-empty list #
# partitions the subset of list from left to right #
PROC partition = ( REF[]INT list, INT left, right, pivot index )INT:
BEGIN
# swaps elements a and b in list #
PROC swap = ( REF[]INT list, INT a, b )VOID:
BEGIN
INT t = list[ a ];
list[ a ] := list[ b ];
list[ b ] := t
END # swap # ;
INT pivot value = list[ pivot index ];
swap( list, pivot index, right );
INT store index := left;
FOR i FROM left TO right - 1 DO
IF list[ i ] < pivot value THEN
swap( list, store index, i );
store index +:= 1
FI
OD;
swap( list, right, store index );
store index
END # partition # ;
INT left := LWB list, right := UPB list, result := 0;
BOOL found := FALSE;
WHILE NOT found DO
IF left = right THEN
result := list[ left ];
found := TRUE
ELSE
INT pivot index = partition( list, left, right, left + ENTIER ( ( random * ( right - left ) + 1 ) ) );
IF k = pivot index THEN
result := list[ k ];
found := TRUE
ELIF k < pivot index THEN
right := pivot index - 1
ELSE
left := pivot index + 1
FI
FI
OD;
result
FI # QSELECT # ;
# test cases #
FOR i TO 10 DO
[ 1 : 10 ]INT test := []INT( 9, 8, 7, 6, 5, 0, 1, 2, 3, 4 );
print( ( whole( i, -2 ), ": ", whole( i QSELECT test, -3 ), newline ) )
OD
END