Reverse String

easy LeetCode #344

two-pointers

Description

Given a string s, reverse it in place. Return the reversed string.

Example 1:
Input: s = "hello"
Output: "olleh"

Example 2:
Input: s = "Hannah"
Output: "hannaH"

Example 3:
Input: s = "a"
Output: "a"
Explanation: Single character remains the same when reversed.

Constraints

1 <= s.length <= 10^5
s consists of printable ASCII characters

Signature

def solution(s: str) -> str: ...

Complexity

Time: O(n)
Space: O(1)

Hints

Pattern: Use two pointers: one at start, one at end
Approach: Swap characters at left and right pointers, then move them toward center
Complexity: Swap elements in place to achieve O(1) extra space

Solutions

char *solution(char *s) {
  if (s[0] == '\0')
    return s;

  size_t i = 0;
  size_t j = strlen(s) - 1;

  while (i < j) {
    char temp = s[i];
    s[i] = s[j];
    s[j] = temp;
    i++;
    j--;
  }

  return s;
}

Python

def solution(s):
    if len(s) == 0:
        return s

    ls = list(s)
    i = 0
    j = len(ls) - 1
    while i < j:
        ls[i], ls[j] = ls[j], ls[i]
        i += 1
        j -= 1
    return "".join(ls)