Update README_EN.md

Author: yanglbme

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

@@ -246,4 +246,48 @@ int sumOfLeftLeaves(struct TreeNode* root) {
 
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+### Solution 2
+
+<!-- tabs:start -->
+
+```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 = 0;
+        stack<TreeNode*> stk{{root}};
+        while (!stk.empty()) {
+            root = stk.top(), stk.pop();
+            if (root->left) {
+                if (!root->left->left && !root->left->right) {
+                    ans += root->left->val;
+                } else {
+                    stk.push(root->left);
+                }
+            }
+            if (root->right) {
+                stk.push(root->right);
+            }
+        }
+        return ans;
+    }
+};
+```
+
+<!-- tabs:end -->
+
 <!-- end -->