fix: Boundary condition of $26 remove-duplicates-from-sorted-… (#323)

boundary condition & update c++ and js code

Author: dorapocket

problems/26.remove-duplicates-from-sorted-array.md

@@ -64,9 +64,11 @@ for (int i = 0; i < len; i++) {
 
 - 如果是数据是无序的，就不可以用这种方式了，从这里也可以看出排序在算法中的基础性和重要性。
 
+- 注意nums为空时的边界条件。
+
 ## 代码
 
-* 语言支持：JS，Python
+* 语言支持：JS，Python，C++
 
 Javascript Code:
 ```js
@@ -76,6 +78,7 @@ Javascript Code:
  */
 var removeDuplicates = function(nums) {
     const size = nums.length;
+    if(size==0) return 0;
     let slowP = 0;
     for (let fastP = 0; fastP < size; fastP++) {
         if (nums[fastP] !== nums[slowP]) {
@@ -101,3 +104,24 @@ class Solution:
         else:
             return 0
 ```
+
+C++ Code:
+```cpp
+class Solution {
+public:
+    int removeDuplicates(vector<int>& nums) {
+        if(nums.empty()) return 0;
+        int fast,slow;
+        fast=slow=0;
+        while(fast!=nums.size()){
+            if(nums[fast]==nums[slow]) fast++;
+            else {
+                slow++;
+                nums[slow]=nums[fast];
+                fast++;
+            }
+        }
+        return slow+1;
+    }
+};
+```