Transcript Sorting - Hiram College

Sorting
Why Sort?
• Put matching elements together
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Uniqueness testing
Deleting duplicates
Frequency Counting
Set operations
• Prioritize Elements
• Reconstruct original order
• Efficient searching (binary search, pairs)
Sorting Algorithms (pp. 80-82)
• Insertion Sort
– Least code, least data movement (inversions)
• Selection Sort
– Conceptually simple, fewest swaps
• Quick Sort
– Fastest
– Needs careful implementation
– Partition algorithm useful on its own
Comparison Functions
• Use with generalized sorting algorithms
• Stable Sort
– Sort criteria separately (most important last)
• Unstable Sort
– Previously sorted not necessarily still in order
– One comparison function handles all criteria
Sorting in C++ (STL)
• Library functions sort and stable_sort
– Iterator bg (beginning of list)
– Iterator end (end of list)
– Optional BinaryPredicate (default <=)
• Function that takes two items and returns true if
they are in order
Sorting in Java
• In java.util.Arrays
– Array of Objects (Object[] a)
– Optional Comparator (default <=)
Search
• Sequential Search
• Binary Search
– Tricky to get right under pressure
• Consider stopping condition
– Library functions
• C++ STL: bsearch
• Java: binarySearch
• (see pp. 84-85)
Generalizing Search
• Sequential
– Foreach element
• If ( correct(element) ) process and break
• Binary
– While (remaining list not empty)
• If (too-high (middle-of-list))
– Cut off bottom half
• Else if (too-low (middle-of-list))
– Cut off top half
• Else process and break
Notes on Binary Search
• Generalized functions “too-high” and “toolow” might evaluate criteria other than a value
– E.g. outcome of function with a given parameter
• If you can estimate a location better than the
middle, use it! (phone book search)