add mergeSort algorithm

Author: sylucky

5.mergeSort.md

@@ -35,8 +35,71 @@
 
 ![动图演示](res/mergeSort.gif)
 
+## 4. C++代码实现
 
-## 4. JavaScript 代码实现
+```cpp
+void merge(vector<int> vec, vector<int>::iterator start, vector<int>::iterator mid, vector<int>::iterator end, vector<int> result)
+{
+    int i = 0;
+    auto leftStart = start;
+    auto rightStart = mid + 1;
+    while (leftStart <= mid && rightStart <= end)
+    {
+        if (*leftStart < *rightStart)
+            result[i++] = *(leftStart++);
+        else
+            result[i++] = *(rightStart++);
+    }
+    while (leftStart <= mid)
+    {
+        result[i++] = *(leftStart++);
+    }
+    while (rightStart <= end)
+    {
+        result[i++] = *(rightStart++);
+    }
+
+    for (int j=0;j<i;j++)
+    {
+        cout << ",i=" << i << ",j=" << j << endl;
+        *(start++) = result[j];
+        cout << *(start - 1) << endl;
+    }
+}
+void mergeSortA(vector<int> vec, vector<int>::iterator start, vector<int>::iterator end, vector<int> result)
+{
+    int mid = 0;
+    if (end > start)
+    {
+        mid = (end - start ) / 2;
+        //左边排序
+        mergeSortA(vec, start, start + mid, result);
+        //右边排序
+        mergeSortA(vec, start + mid + 1, end, result);
+        //合并
+        merge(vec, start, start+mid, end, result);
+    }
+}
+
+vector<int> AlgorithmSort::mergeSort(vector<int> vec)
+{
+    int len = vec.size();
+    //边界值判定
+    if (len <= 1)
+        return vec;
+
+    vector<int> result(len);
+    /*
+        左边与右边排序，再做归并
+    */
+    mergeSortA(vec, vec.begin(), vec.end()-1, result);
+
+    return vec;
+}
+
+```
+
+## 5. JavaScript 代码实现
 
 ```js
 function mergeSort(arr) {  // 采用自上而下的递归方法
@@ -72,7 +135,7 @@ function merge(left, right)
 }
 ```
 
-## 5. Python 代码实现
+## 6. Python 代码实现
 
 ```python
 def mergeSort(arr):
@@ -97,7 +160,7 @@ def merge(left,right):
     return result
 ```
 
-## 6. Go 代码实现
+## 7. Go 代码实现
 
 ```go
 func mergeSort(arr []int) []int {
@@ -137,7 +200,7 @@ func merge(left []int, right []int) []int {
 }
 ```
 
-## 7. Java 代码实现
+## 8. Java 代码实现
 
 ```java
 public class MergeSort implements IArraySort {
@@ -187,7 +250,7 @@ public class MergeSort implements IArraySort {
 }
 ```
 
-## 8. PHP 代码实现
+## 9. PHP 代码实现
 
 ```php
 function mergeSort($arr)