Reverse String

Question (LC.344)

Given a string, return a reversed string.

Cannot do this in-place since string is immutable in Java.

Example

("") => ""
("ab c") => "c ba"

Brute Force

for n-1 to 0
    add it to the new string

L/R Pointers

swap 0 and n-1 until they collide

Code

public String reverseString(String input) {
    if (input == null || input.length() <= 1) {
        return input;
    }
    char[] rev = input.toCharArray();
    int i = 0, j = input.length() - 1;
    while (i < j) {
        char temp = rev[j];
        rev[j] = rev[i];
        rev[i] = temp;
        i++;
        j--;
    }
    return String.valueOf(rev);
}