Reverse Words

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Time: O(n)

Space: O(n)

Intuition

Reverse the words in a sentence. Split by spaces, reverse word list, join.

Algorithm

1Split on whitespace. Reverse array of words. Join with single space.

Common Pitfalls

•Handle multiple spaces and leading/trailing spaces. Same as LC 151.

Reverse Words.java

Java

// Approach: Split string by spaces, collect non-empty tokens, reverse array, join with single space.
// Time: O(n) Space: O(n)
import java.util.*;

class Solution {
    // Function to reverse words in a given string.
    String reverseWords(String str) {
        Stack<String> st = new Stack<>();
        StringBuilder result = new StringBuilder();

        String[] words = str.split("\\.");

        for (String word : words)
            st.push(word);

        while (!st.isEmpty()) {
            result.append(st.pop());
            if (!st.isEmpty())
                result.append(".");
        }

        return result.toString();
    }
}

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