Searching

1
Searching

• Irena Pevac
• CS501

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Searching

• Searching for key in an unordered array
• Sequential search
• Compare key with every item
• Stop if key is found or end is reached
• Searching for key in an ordered array
• Sequential search
• Compare key with every item
• Stop if key is found or an item with larger value
  is reached or end is reached
• Binary search
• Compare key with item in the middle
• Search further in appropriate half of the array

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Linear Search

• int seqSearch(int x, int n, int key)
• for (int index 0 index lt n index)
• if (key xindex)
• return index // Success!
• return -1

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Linear Search in ordered array

• int linearSearchOrdered (int x, int n, int
  key)
• for (int index 0 index lt n index)
• if (key xindex)
• return index // key found
• else if (key lt xindex)
• return -1 // no need to search
  further
• return -1

5
Binary Search

• Input array x, first, last, and key, all
  integers, where x is an ordered array in the
  range first, , last, and key is the item sought.
• Output index such that xindex key if key is
  in x within the range first, , last, and index
  -1 if key is not in this range of x

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• Binary Search
• int binarySearch(int x, int first, int last,
  int key)
• if (last lt first)
• index -1
• else
• int mid (first last)/2
• if (key xmid)
• index mid
• else if (key lt xmid)
• index binarySearch(x, first,
  mid-1, key)
• else
• index binarySearch(x, mid1, last,
  key)
• return index