Merge pull request #1397 from wzqwtt/tree09

添加（0404.左叶子之和、0513.找树左下角的值）Scala版本

problems/0404.左叶子之和.md

@@ -516,6 +516,44 @@ int sumOfLeftLeaves(struct TreeNode* root){
 }
 ```
 
+## Scala
+
+**递归:**
+```scala
+object Solution {
+  def sumOfLeftLeaves(root: TreeNode): Int = {
+    if(root == null) return 0
+    var midValue = 0
+    if(root.left != null && root.left.left == null && root.left.right == null){
+      midValue = root.left.value
+    }
+    // return关键字可以省略
+    midValue + sumOfLeftLeaves(root.left) + sumOfLeftLeaves(root.right)
+  }
+}
+```
+
+**迭代:**
+```scala
+object Solution {
+  import scala.collection.mutable
+  def sumOfLeftLeaves(root: TreeNode): Int = {
+    val stack = mutable.Stack[TreeNode]()
+    if (root == null) return 0
+    stack.push(root)
+    var sum = 0
+    while (!stack.isEmpty) {
+      val curNode = stack.pop()
+      if (curNode.left != null && curNode.left.left == null && curNode.left.right == null) {
+        sum += curNode.left.value // 如果满足条件就累加
+      }
+      if (curNode.right != null) stack.push(curNode.right)
+      if (curNode.left != null) stack.push(curNode.left)
+    }
+    sum
+  }
+}
+```
 
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 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0513.找树左下角的值.md

@@ -546,7 +546,50 @@ func findBottomLeftValue(_ root: TreeNode?) -> Int {
 }
 ```
 
+## Scala
 
+递归版本:
+```scala
+object Solution {
+  def findBottomLeftValue(root: TreeNode): Int = {
+    var maxLeftValue = 0
+    var maxLen = Int.MinValue
+    // 递归方法
+    def traversal(node: TreeNode, leftLen: Int): Unit = {
+      // 如果左右都为空并且当前深度大于最大深度，记录最左节点的值
+      if (node.left == null && node.right == null && leftLen > maxLen) {
+        maxLen = leftLen
+        maxLeftValue = node.value
+      }
+      if (node.left != null) traversal(node.left, leftLen + 1)
+      if (node.right != null) traversal(node.right, leftLen + 1)
+    }
+    traversal(root, 0)  // 调用方法
+    maxLeftValue    // return关键字可以省略
+  }
+}
+```
+
+层序遍历:
+```scala
+  import scala.collection.mutable
+
+  def findBottomLeftValue(root: TreeNode): Int = {
+    val queue = mutable.Queue[TreeNode]()
+    queue.enqueue(root)
+    var res = 0   // 记录每层最左侧结果
+    while (!queue.isEmpty) {
+      val len = queue.size
+      for (i <- 0 until len) {
+        val curNode = queue.dequeue()
+        if (i == 0) res = curNode.value // 记录最最左侧的节点
+        if (curNode.left != null) queue.enqueue(curNode.left)
+        if (curNode.right != null) queue.enqueue(curNode.right)
+      }
+    }
+    res // 最终返回结果，return关键字可以省略
+  }
+```
 
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 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>