The challenge
Write a function that reverses a string. The input string is given as an array of characters char[].
Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.
You may assume all the characters consist of printable ascii characters.
Example 1:
Input: ["h","e","l","l","o"] Output: ["o","l","l","e","h"]
Example 2:
Input: ["H","a","n","n","a","h"] Output: ["h","a","n","n","a","H"]
The solution
The goal here is to not create a new array, or string, but to rather make the change in-place using the single character array.
class Solution {
// the input char array
public void reverseString(char[] s) {
// loop through the array, but only the first half
for (int i=0; i<s.length/2; i++) {
// create a tmp var for first and last
char first = s[i];
char last = s[s.length-1-i];
// swap the variables around
s[i] = last;
s[s.length-1-i] = first;
}
}
}