@@ -0,0 +1,90 @@
+import math
+
+class SegmentTree:
+
+def __init__(self, N):
+self.N = N
+self.st = [0 for i in range(0,4*N)] # approximate the overall size of segment tree with array N
+self.lazy = [0 for i in range(0,4*N)] # create array to store lazy update
+self.flag = [0 for i in range(0,4*N)] # flag for lazy update
+
+def left(self, idx):
+return idx*2
+
+def right(self, idx):
+return idx*2 + 1
+
+def build(self, idx, l, r, A):
+if l==r:
+self.st[idx] = A[l-1]
+else :
+mid = (l+r)//2
+self.build(self.left(idx),l,mid, A)
+self.build(self.right(idx),mid+1,r, A)
+self.st[idx] = max(self.st[self.left(idx)] , self.st[self.right(idx)])
+
+# update with O(lg N) (Normal segment tree without lazy update will take O(Nlg N) for each update)
+def update(self, idx, l, r, a, b, val): # update(1, 1, N, a, b, v) for update val v to [a,b]
+if self.flag[idx] == True:
+self.st[idx] = self.lazy[idx]
+self.flag[idx] = False
+if l!=r:
+self.lazy[self.left(idx)] = self.lazy[idx]
+self.lazy[self.right(idx)] = self.lazy[idx]
+self.flag[self.left(idx)] = True
+self.flag[self.right(idx)] = True
+
+if r < a or l > b:
+return True
+if l >= a and r <= b :
+self.st[idx] = val
+if l!=r:
+self.lazy[self.left(idx)] = val
+self.lazy[self.right(idx)] = val
+self.flag[self.left(idx)] = True
+self.flag[self.right(idx)] = True
+return True
+mid = (l+r)//2
+self.update(self.left(idx),l,mid,a,b,val)
+self.update(self.right(idx),mid+1,r,a,b,val)
+self.st[idx] = max(self.st[self.left(idx)] , self.st[self.right(idx)])
+return True
+
+# query with O(lg N)
+def query(self, idx, l, r, a, b): #query(1, 1, N, a, b) for query max of [a,b]
+if self.flag[idx] == True:
+self.st[idx] = self.lazy[idx]
+self.flag[idx] = False
+if l != r:
+self.lazy[self.left(idx)] = self.lazy[idx]
+self.lazy[self.right(idx)] = self.lazy[idx]
+self.flag[self.left(idx)] = True
+self.flag[self.right(idx)] = True
+if r < a or l > b:
+return -math.inf
+if l >= a and r <= b:
+return self.st[idx]
+mid = (l+r)//2
+q1 = self.query(self.left(idx),l,mid,a,b)
+q2 = self.query(self.right(idx),mid+1,r,a,b)
+return max(q1,q2)
+
+def showData(self):
+showList = []
+for i in range(1,N+1):
+showList += [self.query(1, 1, self.N, i, i)]
+print (showList)
+
+
+if __name__ == '__main__':
+A = [1,2,-4,7,3,-5,6,11,-20,9,14,15,5,2,-8]
+N = 15
+segt = SegmentTree(N)
+segt.build(1,1,N,A)
+print (segt.query(1,1,N,4,6))
+print (segt.query(1,1,N,7,11))
+print (segt.query(1,1,N,7,12))
+segt.update(1,1,N,1,3,111)
+print (segt.query(1,1,N,1,15))
+segt.update(1,1,N,7,8,235)
+segt.showData()