[At Coder] Solve the ABC182 D problem with Ruby

problem

AtCoder Beginner Contest 182

D - Wandering

Given the sequence $ A_1, A_2, A_3, ..., A_N $. This sequence may contain negative elements. The robot located at the coordinate $ 0 $ on the number line performs the following operations in order.

Go forward $ A_1 $ in the positive direction. Advance $ A_1 $ in the positive direction and $ A_2 $ in the positive direction. Forward $ A_1 $ in the positive direction, $ A_2 $ in the positive direction, and $ A_3 $ in the positive direction. ⋮ Forward $ A_1 $ in the positive direction, $ A_2 $ in the positive direction, $ A_3 $ in the positive direction, $ ... $, $ A_N $ in the positive direction.

Find the maximum value of the robot coordinates from the start to the end of the operation.

Constraint

1≦N≦200000 -10^8≦A_i≦10^8 All inputs are integers

input

N A_1 A_2 A_3 ... A_N

Answer

n = gets.chomp.to_i
a = gets.chomp.split.map(&:to_i)

#Coordinates of the robot after operation
position = 0

#Amount of movement due to movement
total_move = 0

#Maximum value of coordinates from start to end when the operation starts at coordinate 0
max_move = 0

#Maximum value of robot coordinates
max_pos = 0

a.each do |move|
    total_move += move
    if total_move > max_move
        max_move = total_move
    end
    if position + max_move > max_pos
        max_pos = position + max_move
    end
    position += total_move
end

puts max_pos