打卡记录

统计区间中的整数数目（动态开点线段树）

链接

class CountIntervals:
    __slots__ = 'left', 'right', 'l', 'r', 'cnt'

    def __init__(self, l=1, r=10 ** 9):
        self.left = self.right = None
        self.l, self.r, self.cnt = l, r, 0

    def add(self, l: int, r: int) -> None:
        if self.cnt == self.r - self.l + 1: return  # self 已被完整覆盖，无需执行任何操作
        if l <= self.l and self.r <= r:  # self 已被区间 [l,r] 完整覆盖，不再继续递归
            self.cnt = self.r - self.l + 1
            return
        mid = (self.l + self.r) // 2
        if self.left is None: self.left = CountIntervals(self.l, mid)  # 动态开点
        if self.right is None: self.right = CountIntervals(mid + 1, self.r)  # 动态开点
        if l <= mid: self.left.add(l, r)
        if mid < r: self.right.add(l, r)
        self.cnt = self.left.cnt + self.right.cnt

    def count(self) -> int:
        return self.cnt