Large language models are increasingly used in competitive programming, and their outputs are sensitive to how a prompt is phrased. Prior work has compared prompt strategies for accuracy on competitive programming, but not for runtime speed, and has not situated the results against human performance. In an exploratory study of one prompt in each of nine styles on GPT-5.5 across three accuracy tasks from the International Olympiad in Informatics (IOI) and two NP-hard speed tasks, we found that no single prompt was best: the strongest prompt depended on the task type and on whether results were summarized by the mean or the median, suggesting that, at least for these tasks, prompt style should be matched to the objective rather than treated as universal. Many differences in mean scores came from a few outlier runs, showing that evaluating prompting by a single metric can obscure how much its effectiveness varies. Compared descriptively with human IOI contestants, who worked under different conditions, the AI was neither strictly better nor strictly worse, exceeding the average contestant on one task but falling short on the other two. By extending prompt comparison from accuracy to runtime speed and grounding it against human performance, this study gives a broader picture of how prompt style affects competitive programming performance.
Figures & tables
Setting
Maximum Clique Size
Number Partitioning
Test input
Random graph on N vertices; each edge included independently with probability N−1/N
5 hours per contest day, shared across three tasks
One response per run
Submissions per task
Up to 50
1 per run
Feedback before resubmitting
Subtask results after each submission
None
Task score
Sum over subtasks of the best result across all submissions
Score of the single submission
TABLE II: Scores and conditions for human IOI contestants and the AI solver on the accuracy tasks.
Prompt
Prisoner Challenge
Message
Migrations
Average
Prompt 1
62.78
30.63
23.68
39.03
Prompt 2
68.89
29.61
22.70
40.40
Prompt 3
63.17
29.94
18.68
37.26
Prompt 4
75.00
30.45
34.16
46.54
Prompt 5
67.44
28.96
26.55
40.98
Prompt 6
79.44
36.26
26.88
47.53
TABLE III: AI accuracy scores by prompt style, scores are out of 100. Mean over 9 iterations per prompt–task pair. Shading compares prompts within each column (green = best, red = worst); bold = column best.
Prompt
Prisoner Challenge
Message
Migrations
Average
Prompt 1
65.00
31.40
20.00
38.80
Prompt 2
65.00
30.33
20.00
38.44
Prompt 3
65.00
29.32
20.00
38.11
Prompt 4
65.00
31.40
28.10
41.50
Prompt 5
65.00
29.32
20.01
38.11
Prompt 6
80.00
31.40
20.00
43.80
TABLE IV: AI accuracy scores by prompt style, scores are out of 100. Median over 9 iterations per prompt–task pair. Shading compares prompts within each column (green = best, red = worst); bold = column best.
Fig. 1: Mean accuracy by prompt style, scores are out of 100 and averaged across the three IOI tasks (Prisoner Challenge, Message, Migrations).
Task
Type
H
p
Holm p
ε2
Prisoner Challenge
Accuracy
19.58
0.012
0.048
0.24
Message
Accuracy
17.16
0.029
0.086
0.21
Migrations
Accuracy
7.07
0.529
1.000
0.09
Maximum Clique Size
Speed
2.35
0.968
1.000
0.03
Number Partitioning †
Speed
20.77
0.008
0.039
0.26
† Confounded with grading order; see Section V-C .
TABLE V: Kruskal-Wallis H test of whether prompt style affected scores on each task (9 prompt styles × 9 runs, 8 degrees of freedom), with Holm-adjusted p -values and effect size ε2 . Shading marks significance at the 0.05 level after Holm adjustment (green = significant, red = not significant); bold = significant before adjustment.
Prompt
Maximum Clique Size
Number Partitioning
Average
Prompt 1
65.35
80.27
72.81
Prompt 2
72.32
79.59
75.96
Prompt 3
69.65
87.30
78.47
Prompt 4
58.74
78.68
68.71
Prompt 5
61.16
78.91
70.04
Prompt 6
62.02
84.58
73.30
TABLE VI: AI speed scores by prompt style, normalized to 100. Maximum completed N within the 1 s time limit, normalized per task; mean over 9 iterations. Shading compares prompts within each column; bold = column best.
Prompt
Maximum Clique Size
Number Partitioning
Average
Prompt 1
67.27
91.84
79.56
Prompt 2
80.00
87.76
83.88
Prompt 3
67.27
87.76
77.52
Prompt 4
58.18
87.76
72.97
Prompt 5
67.27
87.76
77.52
Prompt 6
58.18
87.76
72.97
TABLE VII: AI speed scores by prompt style, normalized to 100. Maximum completed N within the 1 s time limit, normalized per task; median over 9 iterations. Shading compares prompts within each column; bold = column best.
Fig. 2: Mean speed performance by prompt style, normalized to 100 per task and averaged across the two NP-hard optimization tasks (Maximum Clique Size, Number Partitioning).
Fig. 3: AI performance relative to human contestants on the IOI accuracy tasks, scores are out of 100. Bars show the mean score for all contestants, the mean score of gold medalists, and the AI solver (averaged across all nine prompt styles). Contestant and gold-medalist scores were obtained from the official IOI statistics [ 23 , 24 , 25 ] .