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题目：Invert a binary tree. 4 / \ 2 7 / \ / \1 3 6 9to 4 / \ 7 2 / \ / \9 6 3 1Trivia:This problem was inspired byt... 阅读全文
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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.to... 阅读全文
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题目：Implement a basic calculator to evaluate a simple expression string.The expression string may contain open(and closing parentheses), the plus+or mi... 阅读全文