LeetCode 186: Reverse Words in a String II Solution

Master LeetCode problem 186 (Reverse Words in a String II), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

186. Reverse Words in a String II

Medium

Two Pointers String

Problem Explanation

Explanation:

Given a character array s, reverse the order of characters in each word within the array while still preserving whitespace and initial word order.

Algorithm:

Reverse the entire character array s.
Iterate through the reversed array and for each word, reverse the characters to get the original word order.
Finally, reverse the entire array again to get the correct order of words with reversed characters.

Time Complexity: O(n), where n is the length of the character array s. Space Complexity: O(1)

Solution Code

class Solution {
    public void reverseWords(char[] s) {
        reverse(s, 0, s.length - 1);
        
        int start = 0;
        for (int end = 0; end < s.length; end++) {
            if (s[end] == ' ') {
                reverse(s, start, end - 1);
                start = end + 1;
            }
        }
        
        reverse(s, start, s.length - 1);
    }
    
    private void reverse(char[] s, int left, int right) {
        while (left < right) {
            char temp = s[left];
            s[left] = s[right];
            s[right] = temp;
            left++;
            right--;
        }
    }
}

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