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* Retranslate the complete English edition from Simplified Chinese * Polish three English explanations after reader-focused review
70 lines
1.6 KiB
Python
70 lines
1.6 KiB
Python
"""
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File: recursion.py
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Created Time: 2023-08-24
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Author: krahets (krahets@163.com)
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"""
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def recur(n: int) -> int:
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"""Recursion"""
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# Base case
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if n == 1:
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return 1
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# Recurse: make a recursive call
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res = recur(n - 1)
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# Unwind: return the result
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return n + res
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def for_loop_recur(n: int) -> int:
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"""Simulate recursion using iteration"""
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# Use an explicit stack to simulate the system call stack
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stack = []
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res = 0
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# Simulate the recursive-call phase
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for i in range(n, 0, -1):
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# Simulate recursive calls by pushing onto the stack
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stack.append(i)
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# Simulate unwinding and accumulating the result
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while stack:
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# Simulate unwinding by popping from the stack
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res += stack.pop()
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# res = 1+2+3+...+n
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return res
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def tail_recur(n, res):
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"""Tail recursion"""
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# Base case
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if n == 0:
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return res
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# Tail-recursive call
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return tail_recur(n - 1, res + n)
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def fib(n: int) -> int:
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"""Fibonacci sequence: recursion"""
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# Base cases: f(1) = 0, f(2) = 1
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if n == 1 or n == 2:
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return n - 1
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# Recursive calls: f(n) = f(n-1) + f(n-2)
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res = fib(n - 1) + fib(n - 2)
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# Return the result f(n)
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return res
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"""Driver code"""
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if __name__ == "__main__":
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n = 5
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res = recur(n)
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print(f"\nSum from the recursive function: res = {res}")
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res = for_loop_recur(n)
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print(f"\nSum from simulating recursion using iteration: res = {res}")
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res = tail_recur(n, 0)
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print(f"\nSum from the tail-recursive function: res = {res}")
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res = fib(n)
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print(f"\nTerm {n} of the Fibonacci sequence is {res}")
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