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643. Maximum Average Subarray I(python+cpp)

題目:

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].

解釋:
找到陣列nums中均值長度為k的均值最大的subarray的均值,需要注意的是,subsrray是連續的陣列。
不用每次都計算和,首先求出最開始k個數字的和,然後每次只要加上後一個數,再加上後一個數就是新的和了。
python程式碼:

class Solution(object):
    def findMaxAverage(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: float
        """
last_sum=sum(nums[0:k]) max_sum=last_sum for i in xrange(len(nums)-k): last_sum=last_sum+nums[i+k]-nums[i] max_sum=max(max_sum,last_sum) return max_sum/float(k)

c++程式碼:

class Solution {
public:
    double findMaxAverage(vector<int>&
nums, int k) { double last_sum=accumulate(nums.begin(),nums.begin()+k,0); double max_sum=last_sum; for (int i=0;i<nums.size()-k;i++) { last_sum+=nums[i+k]-nums[i]; max_sum=max(max_sum,last_sum); } return max_sum/k; } };

總結:
c++剛開始用int結果最後小數點後幾位精度不對,改成double以後就好了。