151. Reverse Words in a String

Problem Statement

Given an input string s, reverse the order of the words.

A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space.

Return a string of the words in reverse order concatenated by a single space.

Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces.

Examples

Example 1:

• Input: s = "the sky is blue"
• Output: "blue is sky the"

Example 2:

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

Example 3:

• Input: s = "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.

Constraints

• ( 1 \leq s.length \leq 10^4 )
• s contains English letters (upper-case and lower-case), digits, and spaces ' '.
• There is at least one word in s.

Follow-up

If the string data type is mutable in your language, can you solve it in-place with ( O(1) ) extra space?

Solution

func reverseWords(s string) string {
    c := reverseStr([]byte(s))

	var result, word []byte
	for i := 0; i < len(c); i++ {
		if c[i] != ' ' {
			word = append(word, c[i])
		} else if len(word) > 0 {
			result = append(result, reverseStr(word)...)
			word = []byte{}
		}
	}
	return string(result[:len(result)-1])
}

func reverseStr(word []byte) []byte {
	l, r := 0, len(word)-1
	for l < r {
		word[l], word[r] = word[r], word[l]
		l++
		r--
	}
	return append(word, ' ')
}