class Solution {
public void reverseWords(char[] s) {
reverse(s, 0, s.length - 1); // reverse the whole string
reverseWords(s, s.length); // reverse each word
}
private void reverse(char[] s, int l, int r) {
while (l < r) {
final char c = s[l];
s[l++] = s[r];
s[r--] = c;
}
}
private void reverseWords(char[] s, int n) {
int i = 0;
int j = 0;
while (i < n) {
while (i < j || i < n && s[i] == ' ') // skip spaces
++i;
while (j < i || j < n && s[j] != ' ') // skip non spaces
++j;
reverse(s, i, j - 1); // reverse the word
}
}
}