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Lazy Propagation Structure - Segment Trees | Data Structures | Repovive

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Data Structures19 sections · 729 units49h total

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Lazy Propagation Structure

The lazy array

Add a lazy array alongside the tree array:

class LazySegmentTree:
    def __init__(self, n):
        self.n = n
        self.tree = [0] * (4 * n)
        self.lazy = [0] * (4 * n)

lazy[node] stores pending updates that haven't been propagated to children yet.

For "add $v$ to range": lazy[node] means "add $v$ to all elements in this node's range."

Before accessing a node's children, always push down any lazy value first. This guarantees correctness.