feat: add cpp solution to lc problem: No.0404 (doocs#2586)

close doocs#2599

Author: AlleyNawaz

solution/0400-0499/0404.Sum of Left Leaves/README.md

@@ -93,6 +93,37 @@ class Solution {
 }
 ```
 
+```cpp
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    int sumOfLeftLeaves(TreeNode* root) {
+        if (!root) {
+            return 0;
+        }
+        int ans = sumOfLeftLeaves(root->right);
+        if (root->left) {
+            if (!root->left->left && !root->left->right) {
+                ans += root->left->val;
+            } else {
+                ans += sumOfLeftLeaves(root->left);
+            }
+        }
+        return ans;
+    }
+};
+```
+
 ```go
 /**
  * Definition for a binary tree node.

solution/0400-0499/0404.Sum of Left Leaves/README_EN.md

@@ -87,6 +87,37 @@ class Solution {
 }
 ```
 
+```cpp
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    int sumOfLeftLeaves(TreeNode* root) {
+        if (!root) {
+            return 0;
+        }
+        int ans = sumOfLeftLeaves(root->right);
+        if (root->left) {
+            if (!root->left->left && !root->left->right) {
+                ans += root->left->val;
+            } else {
+                ans += sumOfLeftLeaves(root->left);
+            }
+        }
+        return ans;
+    }
+};
+```
+
 ```go
 /**
  * Definition for a binary tree node.

solution/0400-0499/0404.Sum of Left Leaves/Solution.cpp

@@ -0,0 +1,28 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    int sumOfLeftLeaves(TreeNode* root) {
+        if (!root) {
+            return 0;
+        }
+        int ans = sumOfLeftLeaves(root->right);
+        if (root->left) {
+            if (!root->left->left && !root->left->right) {
+                ans += root->left->val;
+            } else {
+                ans += sumOfLeftLeaves(root->left);
+            }
+        }
+        return ans;
+    }
+};