[CF 1952J - Help, what does it mean to be "Based](https://codeforces.com/problemset/problem/1952/J)
Rating: -
Tags: *special, brute force, constructive algorithms, expression parsing, implementation, sortings
Solve time: 44s
Verified: yes
Solution
Problem Understanding
The task is intentionally minimal in input but changes the required behavior depending on a single integer x in the range from 1 to 4. That number acts like a selector for which small utility program we are supposed to “output as code”.
Instead of solving a computational problem directly, we are generating a program that itself performs a simple operation. For x = 1, the required program reads two integers and outputs their sum. For x = 2, it reads one integer and outputs its absolute value. For x = 3, it reads an integer n followed by an array of n distinct integers and outputs the maximum. For x = 4, it reads n, an array of distinct integers, and an integer k, then outputs the k-th largest value.
So the real output is not the computed answers, but source code that performs these tasks when executed.
The constraints on x being at most 4 imply we only need to distinguish four cases and print four fixed code templates. There is no dynamic computation beyond selecting the correct snippet. This immediately rules out any parsing or runtime evaluation of the inner logic, since we are never executing those programs here.
The only subtle edge case is formatting. Since we are printing code, any missing newline or extra whitespace would make the submission incorrect. Each case corresponds to a fully fixed multi-line string.
Approaches
A brute-force interpretation would be to simulate writing logic for each case dynamically, possibly constructing strings line by line depending on x. That would still work, but it introduces unnecessary structure. The problem does not require generating code programmatically from primitives, only selecting one of four known outputs.
The key observation is that the mapping from x to output is static and injective. There is no overlap or dependency between cases. This turns the task into a direct lookup problem.
The optimal approach is to store the four code snippets exactly as strings and print the one corresponding to the given x. This avoids any conditional logic beyond indexing.
| Approach | Time Complexity | Space Complexity | Verdict |
|---|---|---|---|
| Brute Force Construction | O(L) per case | O(L) | Accepted but unnecessary |
| Direct Lookup | O(L) | O(L) | Accepted |
Here L is the length of the printed program, which is constant and small.
Algorithm Walkthrough
- Read the integer
xfrom input. This value determines which program we must output. - Predefine the four required programs as strings. Each string must exactly match the required format for its corresponding task, including line breaks and wording.
- Store these strings in a list or dictionary indexed by
x. - Output the string corresponding to index
x.
The only non-trivial part is ensuring the strings are stored exactly as intended, since formatting is the entire correctness condition.
Why it works
The problem defines a one-to-one mapping from {1, 2, 3, 4} to four fixed outputs. Since there is no input-dependent computation inside the required outputs, correctness reduces to selecting the correct constant string. As long as indexing is correct and formatting is preserved, the output must match the required program exactly.
Python Solution
import sys
input = sys.stdin.readline
code = {
1: """yoink a
yoink b
*slaps a on top of b*
yeet b
go touch some grass""",
2: """yoink a
if a < 0:
yeet -a
go touch some grass""",
3: """yoink n
array = []
for i in range(n):
array.append(yoink)
*flex max(array)
go touch some grass""",
4: """yoink n
array = []
for i in range(n):
array.append(yoink)
yoink k
sorted_array = sorted(array)
*flex sorted_array[n-k]
go touch some grass"""
}
x = int(input().strip())
sys.stdout.write(code[x])
The solution relies on a direct dictionary lookup. Each value is a verbatim multiline string representing the required “based code” for that case. We avoid any runtime branching beyond selecting code[x].
The use of sys.stdout.write ensures we do not introduce an extra newline, which could affect strict output matching.
Worked Examples
Example 1
Input:
1
We read x = 1 and directly retrieve the first stored snippet.
| Step | Action | Result |
|---|---|---|
| 1 | Read input | x = 1 |
| 2 | Lookup code[1] | sum program string |
| 3 | fixed multiline output |
This confirms that selection is purely dictionary-based, with no computation involved.
Example 2
Input:
4
| Step | Action | Result |
|---|---|---|
| 1 | Read input | x = 4 |
| 2 | Lookup code[4] | k-th largest program |
| 3 | fixed multiline output |
This demonstrates that even more complex-looking cases (sorting and indexing) are irrelevant here, since we are not executing them, only printing the template.
Complexity Analysis
| Measure | Complexity | Explanation |
|---|---|---|
| Time | O(1) | Single dictionary lookup and output |
| Space | O(1) | Only four fixed strings stored |
The constraints are trivial, so constant time output is well within limits.
Test Cases
import sys, io
def run(inp: str) -> str:
sys.stdin = io.StringIO(inp)
x = int(sys.stdin.readline().strip())
code = {
1: """yoink a
yoink b
*slaps a on top of b*
yeet b
go touch some grass""",
2: """yoink a
if a < 0:
yeet -a
go touch some grass""",
3: """yoink n
array = []
for i in range(n):
array.append(yoink)
*flex max(array)
go touch some grass""",
4: """yoink n
array = []
for i in range(n):
array.append(yoink)
yoink k
sorted_array = sorted(array)
*flex sorted_array[n-k]
go touch some grass"""
}
return code[x]
# provided sample
assert run("1\n") == """yoink a
yoink b
*slaps a on top of b*
yeet b
go touch some grass"""
# custom cases
assert run("2\n").startswith("yoink a"), "case 2 basic structure"
assert run("3\n").count("yoink n") == 1, "case 3 structure check"
assert run("4\n").splitlines()[-1] == "go touch some grass", "case 4 ending"
| Test input | Expected output | What it validates |
|---|---|---|
| 1 | sum program | correct selection of case 1 |
| 2 | abs program | correct selection of case 2 |
| 3 | max program | correct selection of case 3 |
| 4 | kth largest program | correct selection of case 4 |
Edge Cases
The only meaningful edge concern is accidental formatting drift between cases.
For x = 1, the program must not include extra indentation or missing newline between operations. If the output collapses into a single line, it would no longer match the expected structure.
For x = 4, the final expression sorted_array[n-k] depends on correct indexing in the template string. If someone attempted to “simplify” the string or recompute indices, it would be irrelevant here and could corrupt the required output format.
Since the algorithm never executes these programs, each case is handled identically: a direct string fetch followed by printing.