算法练习(53): 队列、栈或 steque(1.3.47-1.

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算法(第4版)

知识点

• 队列、栈或 steque

题目

1.3.48 双向队列与栈。用一个双向队列实现两个栈，保证每个栈操作只需要常数次的双向队列操作。（请见练习 1.3.33）

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1.3.48 Two stacks with a deque. Implement two stacks with a single deque so that each operation takes a constant number of deque operations (see Exercise 1.3.33).

题目

1.3.49 栈与队列。用有限个栈实现一个队列，保证每个队列操作（在最坏情况下）都只需要常数次的栈操作。

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1.3.49 Queue with three stacks. Implement a queue with three stacks so that each queue operation takes a constant (worst-case) number of stack operations. Warning : high degree of difficulty.

题目

1.3.50 快速出错的迭代器。修改 Stack 的迭代器代码，确保一旦用例在迭代器中（通过 push() 或 pop() 操作）修改集合数据就抛出一个 java.util.ConcurrentModificationException 异常。

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1.3.50 Fail-fast iterator. Modify the iterator code in Stack to immediately throw a java.util.ConcurrentModificationException if the client modifies the collection (via push() or pop()) during iteration? b).
Solution: Maintain a counter that counts the number of push() and pop() operations. When creating an iterator, store this value as an Iterator instance variable. Before each call to hasNext() and next(), check that this value has not changed since con- struction of the iterator; if it has, throw the exception.

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