[LeetCode] 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.

反转字符串中的单词 III。给一个句子，请翻转句子中的所有单词。

思路是前后追击型的双指针。比较靠前的指针在遇到空格的时候就停下，开始做reverse。唯一需要注意的是在遍历完整个input string之后，需要再做一次reverse因为在前的指针只有在遇到空格的时候才会结算/reverse，但是对于最后一个单词，需要额外再处理一次。

时间O(n)

空间O(n) - char array

Java实现

class Solution {
    public String reverseWords(String s) {
        // corner case
        if (s == null || s.length() == 0) {
            return s;
        }

        // normal case
        char[] input = s.toCharArray();
        int i = 0;
        int j = 0;
        while (i < input.length) {
            while (i < input.length && input[i] != ' ') {
                i++;
            }
            reverse(input, j, i - 1);
            while (i < input.length && input[i] == ' ') {
                i++;
            }
            j = i;
        }
        return String.valueOf(input);
    }

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

JavaScript实现

class Solution {
    public String reverseWords(String s) {
        // corner case
        if (s == null || s.length() == 0) {
            return s;
        }

        // normal case
        char[] input = s.toCharArray();
        int i = 0;
        int j = 0;
        while (i < input.length) {
            while (i < input.length && input[i] != ' ') {
                i++;
            }
            reverse(input, j, i - 1);
            while (i < input.length && input[i] == ' ') {
                i++;
            }
            j = i;
        }
        return String.valueOf(input);
    }

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

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