feat: add second js solutions for lcof problems 05 (doocs#357)

Author: shuxiaotai

lcof/面试题05. 替换空格/README.md

@@ -58,6 +58,8 @@ class Solution {
 
 ### **JavaScript**
 
+- 使用字符串内置方法
+
 ```js
 /**
  * @param {string} s
@@ -67,6 +69,37 @@ var replaceSpace = function (s) {
   return s.split(" ").join("%20");
 };
 ```
+- 使用两个指针
+
+```js
+/**
+ * @param {string}
+ * @return {string}
+ */
+var replaceSpace = function(s) {
+  s = s.split("");
+  let emptyNum = 0;
+  for (let i = 0; i < s.length; i++) {
+    if (s[i] === " ") {
+      emptyNum++;
+    }
+  }
+  let p1 = s.length - 1;
+  let p2 = p1 + 2 * emptyNum;
+  while (p1 >= 0 && p2 > p1) {
+    if (s[p1] === " ") {
+      s[p2] = "0";
+      s[--p2] = "2";
+      s[--p2] = "%";
+    } else {
+      s[p2] = s[p1];
+    }
+    p1--;
+    p2--;
+  }
+  return s.join("");
+};
+```
 
 ### **Go**