二刷151

Author: diguage

docs/0151-reverse-words-in-a-string.adoc

@@ -1,56 +1,55 @@
 [#0151-reverse-words-in-a-string]
-= 151. Reverse Words in a String
+= 151. 反转字符串中的单词
 
-{leetcode}/problems/reverse-words-in-a-string/[LeetCode - Reverse Words in a String^]
+https://leetcode.cn/problems/reverse-words-in-a-string/[LeetCode - 151. 反转字符串中的单词 ^]
 
-Given an input string, reverse the string word by word.
+给你一个字符串 `s` ，请你反转字符串中 *单词* 的顺序。
 
- 
+*单词* 是由非空格字符组成的字符串。`s` 中使用至少一个空格将字符串中的 *单词* 分隔开。
 
-*Example 1:*
+返回 *单词* 顺序颠倒且 *单词* 之间用单个空格连接的结果字符串。
 
-[subs="verbatim,quotes,macros"]
-----
-*Input:* "`the sky is blue`"
-*Output:* "`blue is sky the`"
-----
+**注意：**输入字符串 `s`中可能会存在前导空格、尾随空格或者单词间的多个空格。返回的结果字符串中，单词间应当仅用单个空格分隔，且不包含任何额外的空格。
 
-*Example 2:*
-
-[subs="verbatim,quotes,macros"]
-----
-*Input:* "  hello world!  "
-*Output:* "world! hello"
-*Explanation:* Your reversed string should not contain leading or trailing spaces.
-----
+*示例 1：*
 
-*Example 3:*
+....
+输入：s = "the sky is blue"
+输出："blue is sky the"
+....
 
-[subs="verbatim,quotes,macros"]
-----
-*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.
-----
+*示例 2：*
 
- 
+....
+输入：s = "  hello world  "
+输出："world hello"
+解释：反转后的字符串中不能存在前导空格和尾随空格。
+....
 
-*Note:*
+*示例 3：*
 
+....
+输入：s = "a good   example"
+输出："example good a"
+解释：如果两个单词间有多余的空格，反转后的字符串需要将单词间的空格减少到仅有一个。
+....
 
-* 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.
+*提示：*
 
+* `1 \<= s.length \<= 10^4^`
+* `s` 包含英文大小写字母、数字和空格 `+' '+`
+* `s` 中 *至少存在一个* 单词
 
- 
 
-*Follow up:*
+**进阶：**如果字符串在你使用的编程语言中是一种可变数据类型，请尝试使用 stem:[O(1)] 额外空间复杂度的 *原地* 解法。
 
-For C programmers, try to solve it _in-place_ in _O_(1) extra space.
 
 == 思路分析
 
+使用空格切分字符串，然后将字符串对调，再合并。看答案，有个一个更高效的办法，从后面分割单词，这样就不需要对调了。
+
+image::images/0151-10.png[{image_attr}]
+
 [[src-0151]]
 [tabs]
 ====
@@ -63,17 +62,18 @@ include::{sourcedir}/_0151_ReverseWordsInAString.java[tag=answer]
 ----
 --
 
-// 二刷::
-// +
-// --
-// [{java_src_attr}]
-// ----
-// include::{sourcedir}/_0151_ReverseWordsInAString_2.java[tag=answer]
-// ----
-// --
+二刷::
++
+--
+[{java_src_attr}]
+----
+include::{sourcedir}/_0151_ReverseWordsInAString_2.java[tag=answer]
+----
+--
 ====
 
+
 == 参考资料
 
-. https://leetcode.cn/problems/reverse-words-in-a-string/solutions/2361551/151-fan-zhuan-zi-fu-chuan-zhong-de-dan-c-yb1r/?envType=study-plan-v2&envId=selected-coding-interview[151. 反转字符串中的单词 - 双指针，清晰图解^]
+. https://leetcode.cn/problems/reverse-words-in-a-string/solutions/2361551/151-fan-zhuan-zi-fu-chuan-zhong-de-dan-c-yb1r/[151. 反转字符串中的单词 - 双指针，清晰图解^]
 

docs/images/0151-10.png

@@ -943,6 +943,11 @@ endif::[]
 |{doc_base_url}/0150-evaluate-reverse-polish-notation.adoc[题解]
 |✅ 遇到数字就入栈，遇到运算符号就将栈顶元素出栈，计算完成后再入栈。
 
+|{counter:codes2503}
+|{leetcode_base_url}/reverse-words-in-a-string/[151. 反转字符串中的单词^]
+|{doc_base_url}/0151-reverse-words-in-a-string.adoc[题解]
+|✅ 双指针，切割对调。
+
 |===
 
 截止目前，本轮练习一共完成 {codes2503} 道题。

logbook/202503.adoc

@@ -0,0 +1,43 @@
+package com.diguage.algo.leetcode;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class _0151_ReverseWordsInAString_2 {
+  // tag::answer[]
+  /**
+   * @author D瓜哥 · https://www.diguage.com
+   * @since 2025-06-09 21:36:52
+   */
+  public String reverseWords(String s) {
+    List<String> result = new ArrayList<>();
+    int idx = 0;
+    while (idx < s.length()) {
+      int end = s.indexOf(" ", idx);
+      if (end == -1) {
+        result.add(s.substring(idx));
+        break;
+      } else if (idx == end) {
+        idx++;
+      } else {
+        result.add(s.substring(idx, end));
+        idx = end + 1;
+      }
+    }
+    int left = 0, right = result.size() - 1;
+    while (left < right) {
+      String word = result.get(left);
+      result.set(left, result.get(right));
+      result.set(right, word);
+      left++;
+      right--;
+    }
+    return String.join(" ", result);
+  }
+
+  // end::answer[]
+  public static void main(String[] args) {
+    new _0151_ReverseWordsInAString_2()
+      .reverseWords("the sky is blue");
+  }
+}