Reverse the String

Given a string A.

Return the string A after reversing the string word by word.

NOTE:

  1. A sequence of non-space characters constitutes a word.

  2. Your reversed string should not contain leading or trailing spaces, even if it is present in the input string.

  3. If there are multiple spaces between words, reduce them to a single space in the reversed string.



Input Format

The only argument given is string A.
Output Format

Return the string A after reversing the string word by word.
For Example

Input 1:
    A = "the sky is blue"
Output 1:
    "blue is sky the"

Input 2:
    A = "this is ib"
Output 2:
    "ib is this"
Method:

First we reverse the entire string, then we reverse the words one by one

Solution:

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

public class Solution {
    public String solve(String A) {
        StringBuilder result = new StringBuilder();
        char[] arr = A.toCharArray();
        int start = 0;
        int end = arr.length - 1;
        reverse(arr, start, end);
        while (arr[start] == ' ') start ++;
        while (arr[end] == ' ') end --;
        int i = start;
        int j = start;
        while (j <= end + 1) {
            while (j <= end && arr[j] != ' ') j ++;
            reverse(arr, i, j - 1);
            result.append(new String(arr, i, j - i));
            if (j != end + 1) {
                result.append(" ");
            } else {
                break;
            }
            while (j <= end && arr[j] == ' ') j ++;
            i = j;
        }
        return result.toString();
    }
    
    private void reverse(char[] arr, int left, int right) {
        while (left < right) {
            char tmp = arr[left];
            arr[left] = arr[right];
            arr[right] = tmp;
            left ++;
            right --;
        }
    }
}