Merge pull request #281 from xllpiupiu/master

0404左叶子之和JavaScript版本

problems/0404.左叶子之和.md

@@ -226,7 +226,51 @@ class Solution:
 ```
 Go：
 
-
+JavaScript:
+递归版本
+```javascript
+var sumOfLeftLeaves = function(root) {
+    //采用后序遍历 递归遍历
+    // 1. 确定递归函数参数
+    const nodesSum = function(node){
+        // 2. 确定终止条件
+        if(node===null){
+            return 0;
+        }
+        let leftValue = sumOfLeftLeaves(node.left);
+        let rightValue = sumOfLeftLeaves(node.right);
+        // 3. 单层递归逻辑
+        let midValue = 0;
+        if(node.left&&node.left.left===null&&node.left.right===null){
+            midValue = node.left.val;
+        }
+        let sum = midValue + leftValue + rightValue;
+        return sum;
+    }
+    return nodesSum(root);
+};
+```
+迭代版本
+```javascript
+var sumOfLeftLeaves = function(root) {
+   //采用层序遍历
+   if(root===null){
+       return null;
+   }
+   let queue = [];
+   let sum = 0;
+   queue.push(root);
+   while(queue.length){
+     let node = queue.shift();
+     if(node.left!==null&&node.left.left===null&&node.left.right===null){
+         sum+=node.left.val;
+     }
+     node.left&&queue.push(node.left);
+     node.right&&queue.push(node.right);
+   }
+   return sum;
+};
+```