186. Reverse Words in a String II

Given a character array 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 a single space.

Your code must solve the problem in-place, i.e. without allocating extra space.

class Solution {
public:
    void reverseWords(vector<char>& s) {
        int n = s.size(), l = 0, r = n - 1;
        while(l < r) swap(s[l++], s[r--]);
        l = r = 0;
        while(r < n) {
            while(r < n and s[r] != ' ') r++;
            for(int i = l, j = r - 1; i < j; i++, j--) {
                swap(s[i], s[j]);
            }
            l = r = r + 1;
        }
    }
};