solve problem Maximum Average Subarray I

Author: P-ppc

README.md

@@ -175,6 +175,7 @@ All solutions will be accepted!
 |482|[License Key Formatting](https://leetcode-cn.com/problems/license-key-formatting/description/)|[java/py/js](./algorithms/LicenseKeyFormatting)|Easy|
 |720|[Longest Word In Dictionary](https://leetcode-cn.com/problems/longest-word-in-dictionary/description/)|[java/py/js](./algorithms/LongestWordInDictionary)|Easy|
 |836|[Rectangle Overlap](https://leetcode-cn.com/problems/rectangle-overlap/description/)|[java/py/js](./algorithms/RectangleOverlap)|Easy|
+|643|[Maximum Average Subarray I](https://leetcode-cn.com/problems/maximum-average-subarray-i/description/)|[java/py/js](./algorithms/MaximumAverageSubarrayI)|Easy|
 
 # Database
 |#|Title|Solution|Difficulty|

algorithms/MaximumAverageSubarrayI/README.md

@@ -0,0 +1,2 @@
+# Maximum Average Subarray I
+This problem is easy to solve

algorithms/MaximumAverageSubarrayI/Solution.java

@@ -0,0 +1,20 @@
+class Solution {
+    public double findMaxAverage(int[] nums, int k) {
+        int maxSum = 0,
+            curSum = 0,
+            preIndex = -k;
+        
+        for (int num : nums) {
+            if (preIndex < 0) {
+                curSum += num;
+                maxSum = curSum;
+                preIndex++;
+            } else {
+                curSum += num - nums[preIndex++];
+                maxSum = Math.max(maxSum, curSum);
+            }
+        }
+
+        return maxSum * 1.0d / k;
+    }
+}

algorithms/MaximumAverageSubarrayI/solution.js

@@ -0,0 +1,23 @@
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number}
+ */
+var findMaxAverage = function(nums, k) {
+    let maxSum = 0,
+        curSum = 0,
+        preIndex = -k
+    
+    nums.forEach(num => {
+        if (preIndex < 0) {
+            curSum += num
+            maxSum = curSum
+            preIndex++
+        } else {
+            curSum += num - nums[preIndex++]
+            maxSum = Math.max(maxSum, curSum)
+        }
+    })
+    
+    return maxSum / k
+};

algorithms/MaximumAverageSubarrayI/solution.py

@@ -0,0 +1,22 @@
+class Solution(object):
+    def findMaxAverage(self, nums, k):
+        """
+        :type nums: List[int]
+        :type k: int
+        :rtype: float
+        """
+        max_sum = None
+        cur_sum = 0
+        pre_index = None
+        
+        for i in range(len(nums)):
+            if i < k:
+                cur_sum += nums[i]
+                if i == k - 1: max_sum = cur_sum
+            else:
+                pre_index = 0 if pre_index == None else pre_index + 1
+                cur_sum += nums[i] - nums[pre_index]
+                max_sum = max(max_sum, cur_sum)
+                
+        return max_sum * 1.0 / k
+