Maximum Size Subarray Sum Equals k
This is the solution about Leetcode-Maximum Subarray.
Given an array nums and a target value k, find the maximum length of a subarray that sums to k. If there isn’t one, return 0 instead.
The sum of the entire nums array is guaranteed to fit within the 32-bit signed integer range.
Given nums = [1, -1, 5, -2, 3], k = 3,
return 4. (because the subarray [1, -1, 5, -2] sums to 3 and is the longest)
Given nums = [-2, -1, 2, 1], k = 1,
return 2. (because the subarray [-1, 2] sums to 1 and is the longest)
Can you do it in O(n) time?
- Try all possible combinations and get the maximum one.
- Time complexity is O(n^2)
- The main point is we store the sum of 0 - i elements for each location in array. Then we only need to check if sum[j] - sum[i] == k, it represents the sum of i+1 to j.
- We use HashMap to get the constant time for the check stuff.
- Time complexity is O(n+n+n)