Question

Simple task, reverse words in a sentence.

Solution

In Python, this can be simple because of the build-in functions. We can just split the sentence by spaces, reverse the list, and join them with spaces again.

In C++, this can be complicated. The following might be one of the possible answers. We have to scan from the head to tail, and find the position that a word starts and ends. Then reverse the letters in this word. At the end, reverse all the letters in the whole sentence.

Examples

# function to reverse a sentence
def reverse_sentence(sentence):
    return ' '.join(reversed(sentence.split()))

# main
print reverse_sentence("I am a student.")
print reverse_sentence("Testing 1 2 3")
#include <iostream>

using namespace std;

// function to reverse a word, in place
void reverse_word(string* word, int begin, int end)
{
	while (begin < end) {
		char letter = word->at(begin);
		word->at(begin) = word->at(end);
		word->at(end) = letter;
		begin++;
		end--;
	}
}

// function to reverse a sentence, in place
void reverse_sentence(string* sentence)
{
	int length = sentence->size();
	int pointer = 0;
	// for each character
	for (int i = 0; i < sentence->size(); i++) {
		// find word head
		if (pointer == -1) {
			if (sentence->at(i) != ' ') pointer = i;
			continue;
		}
		// find word tail
		if (sentence->at(i) == ' ') {
			reverse_word(sentence, pointer, i - 1);
			pointer = -1;
		}
		// end of string
		if (i == length - 1) {
			reverse_word(sentence, pointer, i - 1);
		}
	}
	// reverse letters for the whole sentence
	reverse_word(sentence, 0, sentence->size() - 1);
}

// main part
int main()
{
	string text = "I am a student.";
	reverse_sentence(&text);
	cout << text << endl;
}
public class InterviewPractice10
{
	private static String reverse_sentence(String sentence)
	{
		String[] splited = sentence.split(" ");
		StringBuilder builder = new StringBuilder();
		for (int i = splited.length - 1; i >= 0; i--) {
			builder.append(splited[i]);
			if (i > 0) builder.append(" ");
		}
		return builder.toString();
	}

	public static void main(String[] args)
	{
		System.out.println(reverse_sentence("I am a student."));
		System.out.println(reverse_sentence("Testing 1 2 3"));
	}
}

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