What is the result of performing the following stack operations starting with an empty stack: push(1), push(2), pop(), push(3), peek()?

Question

BlackTom AI · Accepted Answer

We are given a sequence of stack operations starting from an empty stack, and we must determine the result of performing them: push(1), push(2), pop(), push(3), peek().
First, pushing 1 places 1 on the stack: [1].
Next, pushing 2 places 2 on top: [1, 2]. The top is 2.
Then, pop() removes the top element (2), leaving [1]. The top is now 1.
After that, push(3) places 3 on top: [1, 3]. The top is 3.
Finally, peek() returns the value at the top without removing it, so the result is 3.
Option-by-option analysis:
- None: This would imply no value is produced or the stack has no value to peek, which contradicts the actual top value after the sequence; thus this is incorrect.
- 3: This aligns with the final top value obtained by performing the sequence of operations, so this option is consistent with the result.
- Stack is empty: After performing the pushes and pops, the stack is clearly not empty (it contains 1 and 3 at different times, with 3 on top at the end), so this option is incorrect.
- Error: There is no error in the sequence; all operations are valid on a standard stack, so this option is incorrect.
- 1: While 1 was the bottom element before pushing 3, the final top after the last operation is 3, not 1, making this incorrect.
- 2: The value 2 was popped earlier, and never becomes the top again, so this is incorrect.
In summary, the statement matching the final result produced by the sequence of operations is the option that states 3.

What is the result of performing the following stack operations starting with an empty stack: push(1), push(2), pop(), push(3), peek()?单项选择题

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