557. Reverse Words in a String III

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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.

解法1：

用两个指针指向需要reverse的部分，再分别reverse。把string转化成char array之后比较好操作。
char array到string可以用new string(a)来转化。
C++

1

Java

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public class Solution {
    public String reverseWords(String s) {
        if (s == null || s.length() == 0) {
            return s;
        }
        int start = 0, end = 0;
        char[] ch = s.toCharArray();
        while (end < ch.length) {
            if (ch[end] != ' ') {
                end++;
            } else {
                // reverse substring from start to end
                reverse(ch, start, end - 1);
                while (end < ch.length && ch[end] == ' ') {
                    end++;
                }
                start = end;
            }
        }
        reverse(ch, start, end - 1);
        return new String(ch);
    }
    private void reverse(char[] ch, int start, int end) {
        while (start < end) {
            char temp = ch[start];
            ch[start] = ch[end];
            ch[end] = temp;
            start++;
            end--;
        }
        return;
    }
}