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题目： Implement the following operations of a stack using queues. push(x) -- Push element x onto stack. pop() -- Removes the element on top of the stack 阅读全文
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题目： Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST. Calling next() will return t 阅读全文
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题目： Design a stack that supports push, pop, top, and retrieving the minimum element in constant time. push(x) -- Push element x onto stack. pop() -- R 阅读全文
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题目： Evaluate the value of an arithmetic expression in Reverse Polish Notation. Valid operators are +, -, *, /. Each operand may be an integer or anoth 阅读全文
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题目： Given a binary tree, return the postorder traversal of its nodes' values. For example:Given binary tree {1,#,2,3}, return [3,2,1]. 题意及分析：后序遍历，先遍历左 阅读全文