Merge pull request #1084 from xiaofei-2020/tree17

添加（0513.找树左下角的值.md）：增加typescript版本

problems/0513.找树左下角的值.md

@@ -433,6 +433,51 @@ var findBottomLeftValue = function(root) {
 };
 ```
 
+## TypeScript
+
+> 递归法：
+
+```typescript
+function findBottomLeftValue(root: TreeNode | null): number {
+    function recur(root: TreeNode, depth: number): void {
+        if (root.left === null && root.right === null) {
+            if (depth > maxDepth) {
+                maxDepth = depth;
+                resVal = root.val;
+            }
+            return;
+        }
+        if (root.left !== null) recur(root.left, depth + 1);
+        if (root.right !== null) recur(root.right, depth + 1);
+    }
+    let maxDepth: number = 0;
+    let resVal: number = 0;
+    if (root === null) return resVal;
+    recur(root, 1);
+    return resVal;
+};
+```
+
+> 迭代法：
+
+```typescript
+function findBottomLeftValue(root: TreeNode | null): number {
+    let helperQueue: TreeNode[] = [];
+    if (root !== null) helperQueue.push(root);
+    let resVal: number = 0;
+    let tempNode: TreeNode;
+    while (helperQueue.length > 0) {
+        resVal = helperQueue[0].val;
+        for (let i = 0, length = helperQueue.length; i < length; i++) {
+            tempNode = helperQueue.shift()!;
+            if (tempNode.left !== null) helperQueue.push(tempNode.left);
+            if (tempNode.right !== null) helperQueue.push(tempNode.right);
+        }
+    }
+    return resVal;
+};
+```
+
 ## Swift 
 
 递归版本：