Reverse Words in a String II

Source

• leetcode: 186

Given an input string, reverse the string word by word. A word is defined
as a sequence of non-space characters.

The input string does not contain leading or trailing spaces and the
words are always separated by a single space.

For example,
Given s = "the sky is blue",
return "blue is sky the".
Could you do it in-place without allocating extra space?

Java

public void reverseWords(char[] s) {
    if (s.length == 0) return;
    reverse(s, 0, s.length-1);
    int last = 0;
    for (int i=0; i<s.length; i++) {
        if (s[i] == ' ') {
            reverse(s, last, i-1);
            last = i + 1;
        }
    }
    reverse(s, last, s.length-1)
}

public void reverse(char[] s, int l, int r) {
    while (l <= r) {
        int temp = s[l];
        s[l] = s[r];
        s[r] = temp;
        l++;
        r--;
    }
}