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72 lines
2.2 KiB
Python
72 lines
2.2 KiB
Python
from __future__ import print_function
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import math
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class SegmentTree:
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def __init__(self, A):
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self.N = len(A)
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self.st = [0] * (4 * self.N) # approximate the overall size of segment tree with array N
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self.build(1, 0, self.N - 1)
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def left(self, idx):
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return idx * 2
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def right(self, idx):
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return idx * 2 + 1
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def build(self, idx, l, r):
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if l == r:
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self.st[idx] = A[l]
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else:
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mid = (l + r) // 2
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self.build(self.left(idx), l, mid)
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self.build(self.right(idx), mid + 1, r)
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self.st[idx] = max(self.st[self.left(idx)] , self.st[self.right(idx)])
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def update(self, a, b, val):
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return self.update_recursive(1, 0, self.N - 1, a - 1, b - 1, val)
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def update_recursive(self, idx, l, r, a, b, val): # update(1, 1, N, a, b, v) for update val v to [a,b]
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if r < a or l > b:
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return True
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if l == r :
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self.st[idx] = val
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return True
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mid = (l+r)//2
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self.update_recursive(self.left(idx), l, mid, a, b, val)
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self.update_recursive(self.right(idx), mid+1, r, a, b, val)
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self.st[idx] = max(self.st[self.left(idx)] , self.st[self.right(idx)])
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return True
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def query(self, a, b):
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return self.query_recursive(1, 0, self.N - 1, a - 1, b - 1)
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def query_recursive(self, idx, l, r, a, b): #query(1, 1, N, a, b) for query max of [a,b]
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if r < a or l > b:
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return -math.inf
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if l >= a and r <= b:
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return self.st[idx]
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mid = (l+r)//2
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q1 = self.query_recursive(self.left(idx), l, mid, a, b)
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q2 = self.query_recursive(self.right(idx), mid + 1, r, a, b)
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return max(q1, q2)
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def showData(self):
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showList = []
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for i in range(1,N+1):
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showList += [self.query(i, i)]
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print (showList)
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if __name__ == '__main__':
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A = [1,2,-4,7,3,-5,6,11,-20,9,14,15,5,2,-8]
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N = 15
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segt = SegmentTree(A)
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print (segt.query(4, 6))
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print (segt.query(7, 11))
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print (segt.query(7, 12))
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segt.update(1,3,111)
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print (segt.query(1, 15))
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segt.update(7,8,235)
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segt.showData()
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