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.

Solution 1：

class Solution {

    public String reverseWords(String s) {

        String[] strs = s.split(" ");

        StringBuilder sb = new StringBuilder();

        String space = ""; //此时space不是空格，是"";

        for(String str : strs){ //处理很巧妙，避免空格的多打或者少打

            sb.append(space);

            sb.append(reverse(str)); 

            space = " ";

        }

        return sb.toString();

//或者也可以这样，最后返回值加个trim()

        for(String str : strs){ 

            sb.append(reverse(str)); 

            sb.append( " ");

        }

        return sb.toString().trim();

    }

    

    private String reverse(String s) {

        char[] ch = s.toCharArray();

        int i = 0;

        int j = ch.length - 1;

        while (i < j) {

            char c = ch[i];

            ch[i] = ch[j];

            ch[j] = c;

            i++;

            j--;

        }

        return new String(ch); //字符数组是可以被构建成数组的

    }

}