feat: add typescript solution to lc problem: No.0643.Maximum Average Subarray I (doocs#494)

Author: zhaocchen

solution/0600-0699/0643.Maximum Average Subarray I/README.md

@@ -32,6 +32,8 @@
 
 <!-- 这里可写通用的实现逻辑 -->
 
+滑动窗口
+
 <!-- tabs:start -->
 
 ### **Python3**
@@ -50,6 +52,26 @@
 
 ```
 
+### **TypeScript**
+
+```ts
+function findMaxAverage(nums: number[], k: number): number {
+    let n = nums.length;
+    let ans = 0;
+    let sum = 0;
+    // 前k
+    for (let i = 0; i < k; i++) {
+        sum += nums[i];
+    }
+    ans = sum;
+    for (let i = k; i < n; i++) {
+        sum += (nums[i] - nums[i - k]);
+        ans = Math.max(ans, sum);
+    }
+    return ans / k;
+};
+```
+
 ### **...**
 
 ```

solution/0600-0699/0643.Maximum Average Subarray I/README_EN.md

@@ -59,6 +59,26 @@
 
 ```
 
+### **TypeScript**
+
+```ts
+function findMaxAverage(nums: number[], k: number): number {
+    let n = nums.length;
+    let ans = 0;
+    let sum = 0;
+    // 前k
+    for (let i = 0; i < k; i++) {
+        sum += nums[i];
+    }
+    ans = sum;
+    for (let i = k; i < n; i++) {
+        sum += (nums[i] - nums[i - k]);
+        ans = Math.max(ans, sum);
+    }
+    return ans / k;
+};
+```
+
 ### **...**
 
 ```

solution/0600-0699/0643.Maximum Average Subarray I/Solution.ts

@@ -0,0 +1,15 @@
+function findMaxAverage(nums: number[], k: number): number {
+    let n = nums.length;
+    let ans = 0;
+    let sum = 0;
+    // 前k
+    for (let i = 0; i < k; i++) {
+        sum += nums[i];
+    }
+    ans = sum;
+    for (let i = k; i < n; i++) {
+        sum += (nums[i] - nums[i - k]);
+        ans = Math.max(ans, sum);
+    }
+    return ans / k;
+};