Created
September 29, 2017 11:16
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CSAcademy #050 D. Min Races
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class SegmentTree | |
attr_accessor :n, :dat | |
def initialize(n) | |
@n = n | |
@dat = Array.new(4 * @n - 1, 0) | |
end | |
def update(k, a, node, l, r) | |
if l == r | |
@dat[node] = a | |
return | |
end | |
mid = (l + r) / 2 | |
if k <= mid | |
update(k, a, 2 * node, l, mid) | |
else | |
update(k, a, 2 * node + 1, mid + 1, r) | |
end | |
if @dat[2 * node] > @dat[2 * node + 1] | |
@dat[node] = @dat[2 * node] | |
else | |
@dat[node] = @dat[2 * node + 1] | |
end | |
end | |
def query(a, b, node, l, r) | |
if (r < a) || (b < l) | |
return 0 | |
end | |
if (a <= l) && (r <= b) | |
return @dat[node] | |
end | |
mid = (l + r) / 2 | |
vl = query(a, b, node * 2, l, mid) | |
vr = query(a, b, node * 2 + 1, mid + 1, r) | |
if vl > vr | |
return vl | |
else | |
return vr | |
end | |
end | |
end | |
n, k = gets.chomp.split(" ").map(&:to_i) | |
drivers = Array.new(n) | |
n.times do | |
a, b = gets.chomp.split(" ").map(&:to_i) | |
drivers[b-1] = a | |
end | |
mx = 0 | |
st = SegmentTree.new(n) | |
drivers.each do |cls| | |
v = st.query(cls, n, 1, 1, n) + 1 | |
st.update(cls, v, 1, 1, n) | |
mx = v if v > mx | |
end | |
puts mx |
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