update 209.长度最小的子数组 javascript版本

problems/0209.长度最小的子数组.md

@@ -175,19 +175,24 @@ Go：
 
 
 JavaScript:
-```
-var minSubArrayLen = (target, nums) => {
-    let left = 0, right = 0,win = Infinity,sum = 0;
-    while(right < nums.length){
-       sum += nums[right];
-       while(sum >= target){
-           win = right - left + 1 < win? right - left + 1 : win;
-           sum -= nums[left];
-           left++;
-       }
-       right++;
+
+```js
+
+var minSubArrayLen = function(target, nums) {
+    // 长度计算一次
+    const len = nums.length;
+    let l = r = sum = 0, 
+        res = len + 1; // 子数组最大不会超过自身
+    while(r < len) {
+        sum += nums[r++];
+        // 窗口滑动
+        while(sum >= target) {
+            // r始终为开区间 [l, r)
+            res = res < r - l ? res : r - l;
+            sum-=nums[l++];
+        }
     }
-    return win === Infinity? 0:win;
+    return res > len ? 0 : res;
 };
 ```