🐍1.5write to reverse the string different way

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6 Ways to Reverse a String in Python

Reversing a string is a common coding interview question. Let's explore six different methods to reverse a string in Python, including their explanations, step-by-step breakdowns, and dry runs.

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✅ 1. Using Slicing ([::-1])

def reverse_string(s):
    return s[::-1]

# Example
s = "Python"
print(reverse_string(s))  # Output: "nohtyP"

📝 Explanation

• s[::-1] uses Python's slicing technique.
• The slicing syntax is: s[start:end:step].
  • start: Default (0)
  • end: Default (end of string)
  • step: -1 (moves backwards)

🛠 Dry Run

Index	Character	Action
5	n	First character in reversed string
4	o	Next character
3	h	Next character
2	t	Next character
1	y	Next character
0	P	Last character

Final output: "nohtyP" ✅

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✅ 2. Using reversed() and join()

def reverse_string(s):
    return "".join(reversed(s))

# Example
s = "Python"
print(reverse_string(s))  # Output: "nohtyP"

📝 Explanation

• reversed(s) creates an iterator that iterates over characters in reverse order.
• "".join(...) combines them into a single string.

🛠 Dry Run

• reversed("Python") → ['n', 'o', 'h', 't', 'y', 'P']
• "".join(['n', 'o', 'h', 't', 'y', 'P']) → "nohtyP"

Final output: "nohtyP" ✅

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✅ 3. Using a Loop

def reverse_string(s):
    rev = ""
    for char in s:
        rev = char + rev
    return rev

# Example
s = "Python"
print(reverse_string(s))  # Output: "nohtyP"

📝 Explanation

• Initialize rev = "" (empty string).
• Iterate through each character in s.
• Add each character to the beginning of rev.

🛠 Dry Run

Step	char	rev (Updated Value)
1	P	"P"
2	y	"yP"
3	t	"tyP"
4	h	"htyP"
5	o	"ohtyP"
6	n	"nohtyP"

Final output: "nohtyP" ✅

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✅ 4. Using a while Loop

def reverse_string(s):
    rev = ""
    i = len(s) - 1
    while i >= 0:
        rev += s[i]
        i -= 1
    return rev

# Example
s = "Python"
print(reverse_string(s))  # Output: "nohtyP"

🛠 Dry Run

Step	i (Index)	s[i] (Character)	rev (Updated Value)
1	5	"n"	"n"
2	4	"o"	"no"
3	3	"h"	"noh"
4	2	"t"	"noht"
5	1	"y"	"nohty"
6	0	"P"	"nohtyP"

Final output: "nohtyP" ✅

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✅ 5. Using Recursion

def reverse_string(s):
    if len(s) == 0:
        return s
    return s[-1] + reverse_string(s[:-1])

# Example
s = "Python"
print(reverse_string(s))  # Output: "nohtyP"

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✅ 6. Using Stack (list)

def reverse_string(s):
    stack = list(s)  # Convert string to list
    rev = ""
    while stack:
        rev += stack.pop()  # Remove last element
    return rev

# Example
s = "Python"
print(reverse_string(s))  # Output: "nohtyP"

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🔍 Comparison Table

Method	Code Logic	Time Complexity
Slicing ([::-1])	s[::-1]	O(n)
reversed() + join()	"".join(reversed(s))	O(n)
For Loop	Iterates through string, prepending each character	O(n^2)
While Loop	Iterates backward using an index	O(n)
Recursion	Calls itself with a smaller substring	O(n) (but high memory usage)
Stack (list.pop())	Uses a stack (list) to store and pop characters	O(n)

This table summarizes the different methods with their logic and time complexity. 🚀