186. Reverse Words in a String II

class Solution {
    public void reverseWords(char[] s) {
        int left = 0, right = s.length - 1;
        reverse(s, left, right);
        for (left = 0; left < s.length; left++) {
            if (s[left] == ' ') {
                continue;
            }
            right = left;
            while (right < s.length && s[right] != ' ') {
                right += 1;
            }
            right -= 1;
            reverse(s, left, right);
            left = right;
        }
    }

    private void reverse(char[] s, int left, int right) {
        while (left < right) {
            swap(s, left, right);
            left += 1;
            right -= 1;
        }
    }

    private void swap(char[] s, int i, int j) {
        char temp = s[i];
        s[i] = s[j];
        s[j] = temp;
    }
}

先把整个string reverse, 再把每个word给reverse.

时间复杂度: O(n)
空间复杂度: O(1)