Program to rotate a string of size n, n times to left in Python

Suppose we have a string s of size n. We need to find all rotated strings by rotating them 1 place, 2 places, up to n places to the left.

So, if the input is like s = "hello", then the output will be ['elloh', 'llohe', 'lohel', 'ohell', 'hello']

Approach

To solve this, we will follow these steps −

• Create an empty result list
• Get the length of the string
• For each rotation from 1 to n places:
  • Move the first character to the end
  • Add the rotated string to the result
• Return the result list

Example

Let us see the following implementation to get better understanding −

def solve(s):
    res = []
    n = len(s)
    for i in range(0, n):
        s = s[1:n] + s[0]
        res.append(s)
    return res

s = "hello"
print(solve(s))

The output of the above code is −

['elloh', 'llohe', 'lohel', 'ohell', 'hello']

How It Works

The algorithm works by repeatedly taking the first character of the string and moving it to the end. In each iteration:

• Iteration 1: "hello" ? "elloh" (move 'h' to end)
• Iteration 2: "elloh" ? "llohe" (move 'e' to end)
• Iteration 3: "llohe" ? "lohel" (move 'l' to end)
• Iteration 4: "lohel" ? "ohell" (move 'l' to end)
• Iteration 5: "ohell" ? "hello" (move 'o' to end)

Alternative Approach Using String Slicing

We can also solve this without modifying the original string by using different slice positions ?

def rotate_string(s):
    n = len(s)
    rotations = []
    
    for i in range(1, n + 1):
        # Rotate left by i positions
        rotated = s[i:] + s[:i]
        rotations.append(rotated)
    
    return rotations

s = "hello"
print(rotate_string(s))

The output of the above code is −

['elloh', 'llohe', 'lohel', 'ohell', 'hello']

Conclusion

Both approaches generate all left rotations of a string efficiently. The first method modifies the string iteratively, while the second uses string slicing with different positions for each rotation.