2004ioi教材.ppt

IOI/ACM/ 2004 Training
Session 7
Dr Kan Min-Yen
.sg/~kanmy/talks/040608-IOItraining-
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12 Jun 2004
1
IOI/ACM/ Session 7
Topics and outline
puter Arithmetic and Algebra
Invariants and Number Theory
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12 Jun 2004
2
IOI/ACM/ Session 7
Sorting
Problems and Parameters
Comparison-based sorting
parison-based
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12 Jun 2004
3
IOI/ACM/ Session 7
What sort of problems?
Sorting is usually not the end goal, but a prerequisite
_________
_________
_________
_________
_________
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12 Jun 2004
4
IOI/ACM/ Session 7
Two properties of sorting
Stable
Items with the same value are ordered in the same way after the sort as they were before
Important for doing ____________ sorts
., sorting by First name, Last name
In-place: sorts the items without needing extra space
___________________________________
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12 Jun 2004
5
IOI/ACM/ Session 7
Comparison-based sort
Based paring two items
Many variants, but not the only way to sort
Discuss only the important ones for programming contests
Selection, Insertion, Merge and Quick
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12 Jun 2004
6
IOI/ACM/ Session 7
Comparison Sorts
Comparison Sort Animation: /
Selection
Algo: find min or max of unsorted portion
Heapsort: is selection sort with heap data structure
Remember: ____________________
Insertion
Algo: insert unsorted item in sorted array
Remember: ____________________
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12 Jun 2004
7
IOI/ACM/ Session 7
Comparison Sorts
Merge
Idea: divide and conquer, recursion
Algo: merge two sorted arrays in linear time
Remember: _________________________
Quick
Idea: randomization, pivot
Algo: divide problem to smaller and larger