43 lines
1.9 KiB
Markdown
43 lines
1.9 KiB
Markdown
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## Traffic Light Checker
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A three-color traffic light must switch lights in the following order: red, green, yellow, red.
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To indicate when crossing slowly without a stop is permitted, the yellow signal may be flashed. To indicate when crossing immediately after a full stop is permitted, the red signal may be flashed.
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Either flash sequence may only be started after the red light is lit and must be followed with a red. All lights are initially off. All sequences must begin a red light. Lighting any light causes all other lights to turn off. No color may be repeated: e.g., red, red is not allowed.
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## The problem
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Write a program that checks a sequence of light codes and determines if that sequence follows or violates the traffic light rules.
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Input Read from STDIN a sequence of the follow codes: R (red), Y (yellow), G (Green), P (Pause - flash red), C (Caution - flash yellow), and X (off). Each code must be separated with a space. The entire sequence is submitted by an end-of-line (e.g., pressing the Enter key.) A sequence must have no more than 15 codes in total.
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## Examples
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```text
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1 - Input: R G Y R C R G Y R Output: ACCEPT
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2 - Input: G Y R G Y R Output: REJECT
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3 - Input: R Y G P Output: REJECT
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4 - Input: R G Y Output: ERROR
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5 - Input: X 8 S Output: ERROR
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6 - Input: R G Y R C R P R G Y R G Y R G Y R Output: ERROR
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```
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**Explanation**
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1 - Correct
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2 - Doesn’t start with R
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3 - Invalid sequence
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4 - Undefined code
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5 - Undefined Codes e.g. X is not part of the grammar
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6 - The input is malformed – undefined code, too short, too long, etc
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## Contraints
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Output Write to STDOUT an evaluation of the sequence:
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- ACCEPT >> The entire input sequence meets all rules.
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- REJECT >> The input sequence violates any sequence constraint; for example G Y.
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- ERROR >> The input is malformed – undefined code, too short, too long, etc.
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