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102 lines
2.9 KiB
Python
102 lines
2.9 KiB
Python
from __future__ import annotations
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arr = [-10, -5, 0, 5, 5.1, 11, 13, 21, 3, 4, -21, -10, -5, -1, 0]
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expect = [-5, 0, 5, 5.1, 11, 13, 21, -1, 4, -1, -10, -5, -1, 0, -1]
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def next_greatest_element_slow(arr: list[float]) -> list[float]:
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"""
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Get the Next Greatest Element (NGE) for all elements in a list.
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Maximum element present after the current one which is also greater than the
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current one.
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>>> next_greatest_element_slow(arr) == expect
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True
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"""
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result = []
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arr_size = len(arr)
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for i in range(arr_size):
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next: float = -1
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for j in range(i + 1, arr_size):
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if arr[i] < arr[j]:
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next = arr[j]
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break
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result.append(next)
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return result
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def next_greatest_element_fast(arr: list[float]) -> list[float]:
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"""
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Like next_greatest_element_slow() but changes the loops to use
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enumerate() instead of range(len()) for the outer loop and
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for in a slice of arr for the inner loop.
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>>> next_greatest_element_fast(arr) == expect
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True
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"""
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result = []
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for i, outer in enumerate(arr):
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next: float = -1
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for inner in arr[i + 1 :]:
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if outer < inner:
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next = inner
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break
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result.append(next)
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return result
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def next_greatest_element(arr: list[float]) -> list[float]:
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"""
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Get the Next Greatest Element (NGE) for all elements in a list.
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Maximum element present after the current one which is also greater than the
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current one.
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A naive way to solve this is to take two loops and check for the next bigger
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number but that will make the time complexity as O(n^2). The better way to solve
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this would be to use a stack to keep track of maximum number giving a linear time
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solution.
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>>> next_greatest_element(arr) == expect
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True
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"""
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arr_size = len(arr)
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stack: list[float] = []
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result: list[float] = [-1] * arr_size
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for index in reversed(range(arr_size)):
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if stack:
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while stack[-1] <= arr[index]:
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stack.pop()
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if not stack:
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break
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if stack:
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result[index] = stack[-1]
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stack.append(arr[index])
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return result
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if __name__ == "__main__":
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from doctest import testmod
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from timeit import timeit
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testmod()
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print(next_greatest_element_slow(arr))
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print(next_greatest_element_fast(arr))
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print(next_greatest_element(arr))
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setup = (
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"from __main__ import arr, next_greatest_element_slow, "
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"next_greatest_element_fast, next_greatest_element"
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)
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print(
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"next_greatest_element_slow():",
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timeit("next_greatest_element_slow(arr)", setup=setup),
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)
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print(
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"next_greatest_element_fast():",
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timeit("next_greatest_element_fast(arr)", setup=setup),
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)
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print(
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" next_greatest_element():",
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timeit("next_greatest_element(arr)", setup=setup),
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)
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