643. Maximum Average Subarray I

题目来源【Leetcode】

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].

这道题本质是找给定大小的连续子序列的最大和，用数组来记录前i个数的和再进行比较：

class Solution {public:    double findMaxAverage(vector<int>& nums, int k) {        vector<int>sum;        sum.push_back(0);        int t= 0;        for(int i = 0; i < nums.size(); i++){            t += nums[i];            sum.push_back(t);        }        int re = INT_MIN;        for(int i = 1; i < sum.size()-k+1; i++){              re = max(re,sum[i+k-1]-sum[i-1]);        }        return (double)re/k;    }};