From e9a164add1f9c82318597bfbbc10737f700a8298 Mon Sep 17 00:00:00 2001
From: Flow-sandyu <72751523+Flow-sandyu@users.noreply.github.com>
Date: Mon, 3 Oct 2022 17:59:23 +0800
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时间复杂度 O(n)
参考卡哥 c++ 代码的实现：先移除多余空格，再将整个字符串反转，最后把单词逐个反转
---
 problems/0151.翻转字符串里的单词.md | 68 ++++++++++++++++++++
 1 file changed, 68 insertions(+)

diff --git a/problems/0151.翻转字符串里的单词.md b/problems/0151.翻转字符串里的单词.md
index a848d6a3..5a8f8094 100644
--- a/problems/0151.翻转字符串里的单词.md
+++ b/problems/0151.翻转字符串里的单词.md
@@ -360,6 +360,74 @@ class Solution {
 }
 ```
 
+```java
+/*
+ * 解法四：时间复杂度 O(n)
+ * 参考卡哥 c++ 代码的实现：先移除多余空格，再将整个字符串反转，最后把单词逐个反转
+ */
+class Solution {
+    //用 char[] 来实现 String 的 removeExtraSpaces，reverse 操作
+    public String reverseWords(String s) {
+        char[] chars = s.toCharArray();
+        //1.去除首尾以及中间多余空格
+        chars = removeExtraSpaces(chars);
+        //2.整个字符串反转
+        reverse(chars, 0, chars.length - 1);
+        //3.单词反转
+        reverseEachWord(chars);
+        return new String(chars);
+    }
+
+    //1.用 快慢指针 去除首尾以及中间多余空格，可参考数组元素移除的题解
+    public char[] removeExtraSpaces(char[] chars) {
+        int slow = 0;
+        for (int fast = 0; fast < chars.length; fast++) {
+            //先用 fast 移除所有空格
+            if (chars[fast] != ' ') {
+                //在用 slow 加空格。 除第一个单词外，单词末尾要加空格
+                if (slow != 0)
+                    chars[slow++] = ' ';
+                //fast 遇到空格或遍历到字符串末尾，就证明遍历完一个单词了
+                while (fast < chars.length && chars[fast] != ' ')
+                    chars[slow++] = chars[fast++];
+            }
+        }
+        //相当于 c++ 里的 resize()
+        char[] newChars = new char[slow];
+        System.arraycopy(chars, 0, newChars, 0, slow); 
+        return newChars;
+    }
+
+    //双指针实现指定范围内字符串反转，可参考字符串反转题解
+    public void reverse(char[] chars, int left, int right) {
+        if (right >= chars.length) {
+            System.out.println("set a wrong right");
+            return;
+        }
+        while (left < right) {
+            chars[left] ^= chars[right];
+            chars[right] ^= chars[left];
+            chars[left] ^= chars[right];
+            left++;
+            right--;
+        }
+    }
+
+    //3.单词反转
+    public void reverseEachWord(char[] chars) {
+        int start = 0;
+        //end <= s.length() 这里的 = ，是为了让 end 永远指向单词末尾后一个位置，这样 reverse 的实参更好设置
+        for (int end = 0; end <= chars.length; end++) {
+            // end 每次到单词末尾后的空格或串尾,开始反转单词
+            if (end == chars.length || chars[end] == ' ') {
+                reverse(chars, start, end - 1);
+                start = end + 1;
+            }
+        }
+    }
+}
+```
+
 python:
 
 ```Python