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104 lines
3.1 KiB
Python
104 lines
3.1 KiB
Python
"""
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This is a type of divide and conquer algorithm which divides the search space into
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3 parts and finds the target value based on the property of the array or list
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(usually monotonic property).
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Time Complexity : O(log3 N)
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Space Complexity : O(1)
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"""
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import sys
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# This is the precision for this function which can be altered.
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# It is recommended for users to keep this number greater than or equal to 10.
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precision = 10
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# This is the linear search that will occur after the search space has become smaller.
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def lin_search(left, right, A, target):
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for i in range(left, right + 1):
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if A[i] == target:
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return i
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# This is the iterative method of the ternary search algorithm.
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def ite_ternary_search(A, target):
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left = 0
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right = len(A) - 1
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while True:
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if left < right:
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if right - left < precision:
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return lin_search(left, right, A, target)
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oneThird = (left + right) / 3 + 1
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twoThird = 2 * (left + right) / 3 + 1
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if A[oneThird] == target:
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return oneThird
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elif A[twoThird] == target:
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return twoThird
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elif target < A[oneThird]:
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right = oneThird - 1
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elif A[twoThird] < target:
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left = twoThird + 1
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else:
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left = oneThird + 1
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right = twoThird - 1
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else:
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return None
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# This is the recursive method of the ternary search algorithm.
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def rec_ternary_search(left, right, A, target):
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if left < right:
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if right - left < precision:
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return lin_search(left, right, A, target)
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oneThird = (left + right) / 3 + 1
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twoThird = 2 * (left + right) / 3 + 1
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if A[oneThird] == target:
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return oneThird
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elif A[twoThird] == target:
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return twoThird
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elif target < A[oneThird]:
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return rec_ternary_search(left, oneThird - 1, A, target)
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elif A[twoThird] < target:
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return rec_ternary_search(twoThird + 1, right, A, target)
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else:
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return rec_ternary_search(oneThird + 1, twoThird - 1, A, target)
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else:
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return None
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# This function is to check if the array is sorted.
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def __assert_sorted(collection):
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if collection != sorted(collection):
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raise ValueError("Collection must be sorted")
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return True
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if __name__ == "__main__":
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user_input = input("Enter numbers separated by coma:\n").strip()
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collection = [int(item) for item in user_input.split(",")]
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try:
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__assert_sorted(collection)
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except ValueError:
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sys.exit("Sequence must be sorted to apply the ternary search")
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target_input = input("Enter a single number to be found in the list:\n")
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target = int(target_input)
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result1 = ite_ternary_search(collection, target)
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result2 = rec_ternary_search(0, len(collection) - 1, collection, target)
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if result2 is not None:
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print(f"Iterative search: {target} found at positions: {result1}")
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print(f"Recursive search: {target} found at positions: {result2}")
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else:
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print("Not found")
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