Merge pull request #1392 from xiaofei-2020/extra02

添加（0941.有效的山脉数组.md）：增加typescript版本

problems/0941.有效的山脉数组.md

@@ -157,6 +157,26 @@ var validMountainArray = function(arr) {
 };
 ```
 
+## TypeScript
+
+```typescript
+function validMountainArray(arr: number[]): boolean {
+    const length: number = arr.length;
+    if (length < 3) return false;
+    let left: number = 0,
+        right: number = length - 1;
+    while (left < (length - 1) && arr[left] < arr[left + 1]) {
+        left++;
+    }
+    while (right > 0 && arr[right] < arr[right - 1]) {
+        right--;
+    }
+    if (left === right && left !== 0 && right !== length - 1)
+        return true;
+    return false;
+};
+```
+