Claude
b9aeb78b24
Co-Authored-By: Claude Sonnet 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_017ic4b6nxynun5JFivebVb1
34 lines
1.8 KiB
Plaintext
34 lines
1.8 KiB
Plaintext
Eight classic mistakes, each reproduced
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=======================================
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1. balanced brackets by counting each kind, with no stack
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input "([)]": counts-only = true stack = false
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every count ends at zero, but the ] arrives while the ( is not the innermost open bracket
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2. min stack that compares boxed Integers with ==
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push [10, 20, 5], pop, getMin(): broken = 10 correct = 10
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push [1000, 2000, 500], pop, getMin(): broken = 500 correct = 1000
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Integer.valueOf caches -128..127, so small values share one object and == happens to work
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3. min stack that pushes onto the min stack only on a strictly smaller value
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push 3, push 3, pop, getMin(): strict -> NullPointerException: Cannot invoke "java.lang.Integer.intValue()" because the return value of "java.util.Deque.peek()" is null
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correct -> 3 (the stack still holds one 3)
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4. encoded min stack with int differences instead of long
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push Integer.MIN_VALUE, push Integer.MAX_VALUE, top(): int diffs = -2147483648 long diffs = 2147483647
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MAX_VALUE - MIN_VALUE does not fit in an int, wraps to -1, and -1 looks like "new minimum"
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5. next greater element popping on <= instead of <
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input [2, 2, 3]: buggy = [2, 3, -1] correct = [3, 3, -1]
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the first 2 is told its next greater element is 2
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6. largest rectangle without the final height-0 bar
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input [2, 4]: buggy = 0 correct = 4
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nothing ever pops the bars that are still on the stack when the loop ends
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7. queue from two stacks that pours on every dequeue
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enqueue 1, 2; dequeue; enqueue 3; dequeue: first = 1 (ok), second: broken = 3 correct = 2
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the 3 was poured on top of the 2 that was still waiting in the output stack
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8. popping an empty structure: both conversions throw NoSuchElementException, as ArrayDeque.pop does
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