557. Reverse Words in a String III

二刷 06/2022

Version #1 Char array in-place reverse

Time O(N)

Space O(N)

Runtime: 5 ms, faster than 91.68% of Java online submissions for Reverse Words in a String III.

Memory Usage: 48.8 MB, less than 75.85% of Java online submissions for Reverse Words in a String III.

class Solution {

    public String reverseWords(String s) {

        // s   f

        // abc def

        char[] chars = s.toCharArray();

        int slow = 0, fast = 0;

        while (fast <= chars.length) {

            if (fast == chars.length || chars[fast] == ' ') {

                reverse(chars, slow, fast - 1);

                slow = fast + 1;

            }

            fast++;

        }

        return new String(chars);

    }

    private void reverse(char[] chars, int start, int end) {

        while (start < end) {

            char c = chars[start];

            chars[start] = chars[end];

            chars[end] = c;

            start++;

            end--;

        }

    }

}

Version #2 StringBuilder reverse function

Time O(N)

Space O(N)

Runtime: 4 ms, faster than 96.93% of Java online submissions for Reverse Words in a String III.

Memory Usage: 42.9 MB, less than 87.56% of Java online submissions for Reverse Words in a String III.

class Solution {

    public String reverseWords(String s) {

        String[] parts = s.split(" ");

        StringBuilder sb = new StringBuilder();

        for (String part : parts) {

            sb.append(new StringBuilder(part).reverse().toString());

            sb.append(" ");

        }

        return sb.toString().trim();

    }

}

一刷

40.36 %

class Solution {
    public String reverseWords(String s) {
        if (s == null || s.length() == 0) {
            return s;
        }
        String[] strs = s.split("\\s+");
        StringBuilder sb = new StringBuilder();
        for (String str : strs) {
            sb.append(" ").append(reverse(str));
        }
        return sb.length() == 0 ? "" : sb.substring(1).toString();
    }
   
    private String reverse(String str) {
        char[] chars = str.toCharArray();
        int left = 0;
        int right = chars.length - 1;
        while (left < right) {
            char temp = chars[left];
            chars[left] = chars[right];
            chars[right] = temp;
            left++;
            right--;
        }
        return new String(chars);
    }
}