From 51e719a4351fb97ed41ad6995bc6470d5204ad35 Mon Sep 17 00:00:00 2001
From: Eyjan_Huang <81480748+Eyjan-Huang@users.noreply.github.com>
Date: Thu, 19 Aug 2021 17:57:39 +0800
Subject: [PATCH] =?UTF-8?q?=E7=AE=80=E5=8C=96=20=E5=89=91=E6=8C=87Offer05.?=
 =?UTF-8?q?=E6=9B=BF=E6=8D=A2=E7=A9=BA=E6=A0=BC.md=20python=E4=BB=A3?=
 =?UTF-8?q?=E7=A0=81?=
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减少不必要的变量使用，优化空间复杂度，使用切片替换而不是单个替换
---
 problems/剑指Offer05.替换空格.md | 58 +++++++++-----------------
 1 file changed, 20 insertions(+), 38 deletions(-)

diff --git a/problems/剑指Offer05.替换空格.md b/problems/剑指Offer05.替换空格.md
index 4ae5f9f2..3f373d0d 100644
--- a/problems/剑指Offer05.替换空格.md
+++ b/problems/剑指Offer05.替换空格.md
@@ -202,45 +202,27 @@ func replaceSpace(s string) string {
 
 python：
 ```python
-class Solution(object):
-    def replaceSpace(self, s):
-        """
-        :type s: str
-        :rtype: str
-        """
-        list_s = list(s)
-
-        # 记录原本字符串的长度
-        original_end = len(s)
-
-        # 将空格改成%20 使得字符串总长增长 2n，n为原本空格数量。
-        # 所以记录空格数量就可以得到目标字符串的长度
-        n_space = 0
-        for ss in s:
-            if ss == ' ':
-                n_space += 1
-                
-        list_s += ['0'] * 2 * n_space
-
-        # 设置左右指针位置
-        left, right = original_end - 1, len(list_s) - 1
-
-        # 循环直至左指针越界
-        while left >= 0:
-            if list_s[left] == ' ':
-                list_s[right] = '0'
-                list_s[right - 1] = '2'
-                list_s[right - 2] = '%'
-                right -= 3
-            else:
-                list_s[right] = list_s[left]
-                right -= 1
-            
-            left -= 1
+class Solution:
+    def replaceSpace(self, s: str) -> str:
+        counter = s.count(' ')
         
-        # 将list变回str，输出
-        s = ''.join(list_s)
-        return s
+        res = list(s)
+        # 每碰到一个空格就多拓展两个格子，1 + 2 = 3个位置存’%20‘
+        res.extend([' '] * counter * 2)
+        
+        # 原始字符串的末尾，拓展后的末尾
+        left, right = len(s) - 1, len(res) - 1
+        
+        while left >= 0:
+            if res[left] != ' ':
+                res[right] = res[left]
+                right -= 1
+            else:
+                # [right - 2, right), 左闭右开
+                res[right - 2: right + 1] = '%20'
+                right -= 3
+            left -= 1
+        return ''.join(res)
             
 ```