Introduction to Searching Algorithm for beginners
- 1. SEARCHING
- 2. Vocabulary • List • A collection of heterogeneous data (values can be different types) • Dynamic in size • Array • A collection of homogenous data (values are all the same type) • Static in size • Element • A value in a list or array • Index • A location in the list or array • Key • The search parameter (the element you are looking for)
- 3. Linear Search Algorithm 1. Start from the beginning of the list 2. Check if current element matches key 1. If there is a match, then do whatever you need to do 1. Example: return the current index 2. Example: print a message saying that the key was found 3. Move to next element 4. Repeat steps 2-3 until key is found or end of list is reached 1. If the end of the list is reach and the key is not found, then do whatever you need to do 1. Example: return -1 2. Example: print a message saying that the key was not found
- 4. Linear Search Questions • Does the array need to be sorted for linear search? • Assuming N elements in an array, on average, where will a key be found? • In a best case scenario (key is found immediately), how many comparisons or checks will be done in linear search? • In a worst case scenario (key is not found at all), how many comparisons or checks will be done in linear search?
- 5. Binary Search • Also known as a “dictionary search” • The list/array must be sorted (like a dictionary) • Super fast at finding things
- 6. Binary Search Algorithm 1. Go to the middle element (at the middle index) 2. If the middle element matches the key, then the search is over 3. If the key is less than middle element, go to the left (down), else go to the right (up) 4. Repeat steps 2-4 until key is found or when the left and right bounds pass each other
- 7. Detailed Binary Search Algorithm 1. The left bound variable is initialized to 0 2. The right bound variable is initialized to the last index 3. The middle index is the halfway point between left and right 4. Go to the middle element (at the middle index) 5. If the middle element matches the key, then the search is over 6. If the key is less than middle element, go to the left 1. Set the right bound variable to the middle index – 1 7. If the key is greater than middle element, go to the right 1. Set the left bound variable to the middle index + 1 8. Repeat steps 3-7 while key is not found and while the left bound is less than or equal to the right bound
- 8. Binary Search Questions • Does the array need to be sorted for binary search? • In a best case scenario (key is found immediately), how many comparisons or checks will be done in binary search? • In a worst case scenario (key is not found at all), how many comparisons or checks will be done in binary search? • How much faster is binary search than linear search?