Reverse Words in a String (M)

Given an input string, reverse the string word by word.

Example 1:

Input: "the sky is blue"
Output: "blue is sky the"

Example 2:

Input: "  hello world!  "
Output: "world! hello"
Explanation: Your reversed string should not contain leading or trailing spaces.

Example 3:

Input: "a good   example"
Output: "example good a"
Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string.

Note:

A word is defined as a sequence of non-space characters.
Input string may contain leading or trailing spaces. However, your reversed string should not contain leading or trailing spaces.
You need to reduce multiple spaces between two words to a single space in the reversed string.

题意

将给定字符串中的非空格单词的顺序逆置，要求新字符串中前后无空白字符，且每个单词之间有一个空格。

思路

将字符串中所有单词依次存入栈中，再出栈构建新字符串即可。

代码实现

class Solution {
    public String reverseWords(String s) {
        s = s.trim();
        Deque<String> stack = new ArrayDeque<>();
        StringBuilder sb = new StringBuilder();

        int first = 0, last = 0;
        while (last < s.length()) {
            while (last < s.length() && s.charAt(last) != ' ') {
                last++;
            }
            stack.push(s.substring(first, last));
            while (last < s.length() && s.charAt(last) == ' ') {
                last++;
            }
            first = last;
        }

        for (String word : stack) {
            if (sb.length() == 0) {
                sb.append(word);
            } else {
                sb.append(" " + word);
            }
        }

        return sb.toString();
    }
}

来源：https://blog.csdn.net/mapoos/article/details/100977128

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151. Reverse Words in a String (M)

Reverse Words in a String (M)