Editorial for DMOPC '18 Contest 5 P3 - A Familiar Problem


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Authors: Kirito

For the first subtask, we can iterate over all subarrays \mathcal O(N^2) subarrays, and find their sum in \mathcal O(N) time, keeping track of the longest one where the sum does not exceed M.

Time Complexity: \mathcal O(N^3)

For the second subtask, we can find the sum in \mathcal O(1) time by using a prefix sum array.

Time Complexity: \mathcal O(N^2)

For the third subtask, we can use a 2-pointer approach. As the right pointer advances, the left pointer should point to the left-most index where the sum is less than M. Since both pointers will only move from left to right, the time complexity is \mathcal O(N).

Time Complexity: \mathcal O(N)


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