Editorial for DMOPC '14 Contest 2 P4 - Deforestation


Remember to use this editorial only when stuck, and not to copy-paste code from it. Please be respectful to the problem author and editorialist.

Submitting an official solution before solving the problem yourself is a bannable offence.

We will use a prefix sum array here. Let P[i] be the sum of all masses from element 1 to element i. The sum of all masses from i to j can be expressed as P[j] - P[i] + mass[i]. The preprocessing time is linear and each query takes constant time. Python users having a hard time should try the PyPy interpreter. Fast input and output methods should be used if possible.


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