Created
November 29, 2016 02:18
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| class BinaryIndexedTree | |
| def initialize(n) | |
| @freq = Array.new(n, 0) | |
| @btree = Array.new(n + 1, 0) | |
| end | |
| def sum(index) | |
| sum = 0 | |
| index += 1 | |
| while (index > 0) | |
| sum += @btree[index] | |
| index = sum_parent_fn(index) | |
| end | |
| sum | |
| end | |
| def update(index, newValue) | |
| @freq[index] += newValue | |
| index += 1 | |
| while (index <= @freq.length) | |
| @btree[index] += newValue | |
| index = update_parent_fn(index) | |
| end | |
| end | |
| def freq | |
| @freq | |
| end | |
| private | |
| def sum_parent_fn(index) | |
| index - (index & -index) | |
| end | |
| def update_parent_fn(index) | |
| index + (index & -index) | |
| end | |
| end | |
| tree = BinaryIndexedTree.new(13) | |
| skyline = [ | |
| [2, 9, 10], | |
| [3, 7, 15], | |
| [5, 12, 12] | |
| ] | |
| skyline.each do |left, right, height| | |
| curr_left_height = tree.sum(left) | |
| curr_right_height = tree.sum(right) | |
| if curr_left_height < height | |
| tree.update(left, height - curr_left_height) | |
| end | |
| if curr_right_height < height | |
| tree.update(right, curr_right_height - height) | |
| end | |
| end | |
| puts "freq: #{tree.freq.to_s}" |
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