添加（0111.二叉树的最小深度.md）：增加typescript版本

Author: xiaofei-2020

problems/0111.二叉树的最小深度.md

@@ -404,6 +404,44 @@ var minDepth = function(root) {
 };
 ```
 
+## TypeScript
+
+> 递归法
+
+```typescript
+function minDepth(root: TreeNode | null): number {
+    if (root === null) return 0;
+    if (root.left !== null && root.right === null) {
+        return 1 + minDepth(root.left);
+    }
+    if (root.left === null && root.right !== null) {
+        return 1 + minDepth(root.right);
+    }
+    return 1 + Math.min(minDepth(root.left), minDepth(root.right));
+}
+```
+
+> 迭代法
+
+```typescript
+function minDepth(root: TreeNode | null): number {
+    let helperQueue: TreeNode[] = [];
+    let resMin: number = 0;
+    let tempNode: TreeNode;
+    if (root !== null) helperQueue.push(root);
+    while (helperQueue.length > 0) {
+        resMin++;
+        for (let i = 0, length = helperQueue.length; i < length; i++) {
+            tempNode = helperQueue.shift()!;
+            if (tempNode.left === null && tempNode.right === null) return resMin;
+            if (tempNode.left !== null) helperQueue.push(tempNode.left);
+            if (tempNode.right !== null) helperQueue.push(tempNode.right);
+        }
+    }
+    return resMin;
+};
+```
+
 ## Swift
 
 > 递归