add 643

Author: fishercoder1534

README.md

@@ -20,6 +20,7 @@ Your ideas/fixes/algorithms are more than welcome!
 
 |  #  |      Title     |   Solutions   | Time          | Space         | Difficulty  | Tag          | Notes
 |-----|----------------|---------------|---------------|---------------|-------------|--------------|-----
+|643|[Maximum Average Subarray I](https://leetcode.com/problems/maximum-average-subarray-i/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_643.java) | O(n) |O(1) | Easy |
 |640|[Solve the Equation](https://leetcode.com/problems/solve-the-equation/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_640.java) | O(n) |O(n) | Medium |
 |638|[Shopping Offers](https://leetcode.com/problems/shopping-offers/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_638.java) | O(2^n) |O(n) | Medium | DP, DFS
 |637|[Average of Levels in Binary Tree](https://leetcode.com/problems/average-of-levels-in-binary-tree/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_637.java) | O(n) |O(1) | Easy | 

src/main/java/com/fishercoder/solutions/_643.java

@@ -0,0 +1,45 @@
+package com.fishercoder.solutions;
+
+/**
+ * 643. Maximum Average Subarray I
+ *
+ * Given an array consisting of n integers, find the contiguous subarray of given length k that has the maximum average value.
+ * And you need to output the maximum average value.
+
+ Example 1:
+ Input: [1,12,-5,-6,50,3], k = 4
+ Output: 12.75
+ Explanation: Maximum average is (12-5-6+50)/4 = 51/4 = 12.75
+ Note:
+ 1 <= k <= n <= 30,000.
+ Elements of the given array will be in the range [-10,000, 10,000].
+ */
+public class _643 {
+
+    public static double findMaxAverage(int[] nums, int k) {
+        double sum = 0;
+        double maxAve = Integer.MIN_VALUE;
+        for (int i = 0; i < nums.length; i++) {
+            if (k <= i) {
+                sum -= nums[i-k];
+            }
+            sum += nums[i];
+            if ((i+1) >= k) {
+                maxAve = Math.max(maxAve, sum / k);
+            }
+        }
+        return maxAve;
+    }
+
+    public static void main(String... args) {
+//        int[] nums = new int[]{1,12,-5,-6,50,3};
+//        int k = 4;
+
+//        int[] nums = new int[]{-1};
+//        int k = 1;
+
+        int[] nums = new int[]{-6662,5432,-8558,-8935,8731,-3083,4115,9931,-4006,-3284,-3024,1714,-2825,-2374,-2750,-959,6516,9356,8040,-2169,-9490,-3068,6299,7823,-9767,5751,-7897,6680,-1293,-3486,-6785,6337,-9158,-4183,6240,-2846,-2588,-5458,-9576,-1501,-908,-5477,7596,-8863,-4088,7922,8231,-4928,7636,-3994,-243,-1327,8425,-3468,-4218,-364,4257,5690,1035,6217,8880,4127,-6299,-1831,2854,-4498,-6983,-677,2216,-1938,3348,4099,3591,9076,942,4571,-4200,7271,-6920,-1886,662,7844,3658,-6562,-2106,-296,-3280,8909,-8352,-9413,3513,1352,-8825};
+        int k = 90;
+        System.out.println(findMaxAverage(nums, k));
+    }
+}