557. Reverse Words in a String III

Given a string, you need to reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.

Example 1:

Input: "Let's take LeetCode contest"
Output: "s'teL ekat edoCteeL tsetnoc"

Note: In the string, each word is separated by single space and there will not be any extra space in the string.

time: O(n), space: O(1)

class Solution {
    public String reverseWords(String s) {
        String[] strs = s.split(" ");
        StringBuilder sb = new StringBuilder();
        for(String str : strs) {
            StringBuilder tmp = new StringBuilder(str);
            sb.append(tmp.reverse().append(" "));
        }
        return sb.toString().trim();
    }
}

faster, time: O(n), space: O(1)

class Solution {
    public String reverseWords(String s) {
        char[] str = s.toCharArray();
        int i = 0, j = 0;
        while(j < str.length) {
            if(str[j] == ' ') {
                reverse(str, i, j - 1);
                j++;
                i = j;
            } else {
                j++;
            }
        }
        reverse(str, i, j - 1);     // last word
        return new String(str);
    }
    
    private void reverse(char[] c, int i, int j) {
        while(i < j) {
            char tmp = c[i];
            c[i] = c[j];
            c[j] = tmp;
            i++;
            j--;
        }
    }
}