151. Reverse Words in a String #

Problem #

Given an input string, reverse the string word by word.

Example 1:

Input: "the sky is blue"
Output: "blue is sky the"

Example 2:

Input: "  hello world!  "
Output: "world! hello"
Explanation: Your reversed string should not contain leading or trailing spaces.

Example 3:

Input: "a good   example"
Output: "example good a"
Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string.

Note:

• A word is defined as a sequence of non-space characters.
• Input string may contain leading or trailing spaces. However, your reversed string should not contain leading or trailing spaces.
• You need to reduce multiple spaces between two words to a single space in the reversed string.

Follow up:

For C programmers, try to solve it in-place in O(1) extra space.

Problem Summary #

Given a string, reverse each word in the string one by one.

Explanation:

• A word is composed of non-space characters.
• The input string may contain extra spaces at the beginning or end, but the reversed string must not include them.
• If there are extra spaces between two words, reduce the spaces between words after reversal to just one.  

Follow-up:

• Users choosing the C language are asked to try using an in-place solution with O(1) extra space complexity.

Solution Approach #

• Given a string with words separated by spaces, reverse the string in terms of words.
• According to the problem statement, first split the string into individual words by spaces, then reverse the order of the words, and finally add spaces between each word.

Code #

package leetcode

import "strings"

func reverseWords151(s string) string {
	ss := strings.Fields(s)
	reverse151(&ss, 0, len(ss)-1)
	return strings.Join(ss, " ")
}

func reverse151(m *[]string, i int, j int) {
	for i <= j {
		(*m)[i], (*m)[j] = (*m)[j], (*m)[i]
		i++
		j--
	}
}