We use a helper function with two pointers l and r. We swap s[l] and s[r] and then recurse for the inner part of the string.

1. Helper function solve(l, r):
   • Base case: If l >= r, return.
   • Swap s[l] and s[r].
   • solve(l + 1, r - 1).
2. Call solve(0, len(s) - 1).

• Time Complexity: O(N).
• Space Complexity: O(N) (stack).

def reverse_string(s):
    def solve(l, r):
        if l >= r:
            return
        s[l], s[r] = s[r], s[l]
        solve(l + 1, r - 1)
        
    solve(0, len(s) - 1)