Datasets:
Tasks:
Text Generation
Modalities:
Text
Formats:
json
Languages:
English
Size:
< 1K
ArXiv:
Tags:
competitive-programming
code-generation
specification-generation
proof-generation
verification
rust
License:
| use vstd::prelude::*; | |
| fn main() {} | |
| verus! { | |
| pub struct Solution; | |
| pub open spec fn prefix_sum(a: Seq<u64>, end: int) -> int | |
| recommends | |
| 0 <= end <= a.len(), | |
| decreases end, | |
| { | |
| if end <= 0 { | |
| 0int | |
| } else { | |
| prefix_sum(a, end - 1) + a[end - 1] as int | |
| } | |
| } | |
| pub open spec fn prefix_max(a: Seq<u64>, end: int) -> int | |
| recommends | |
| 1 <= end <= a.len(), | |
| decreases end, | |
| { | |
| if end <= 1 { | |
| a[0] as int | |
| } else { | |
| let prev = prefix_max(a, end - 1); | |
| let v = a[end - 1] as int; | |
| if v > prev { v } else { prev } | |
| } | |
| } | |
| pub open spec fn count_good_prefixes(a: Seq<u64>, end: int) -> int | |
| recommends | |
| 0 <= end <= a.len(), | |
| decreases end, | |
| { | |
| if end <= 0 { | |
| 0int | |
| } else { | |
| let prev = count_good_prefixes(a, end - 1); | |
| let s = prefix_sum(a, end); | |
| let m = prefix_max(a, end); | |
| if 2 * m == s { | |
| prev + 1 | |
| } else { | |
| prev | |
| } | |
| } | |
| } | |
| impl Solution { | |
| pub fn count_good_prefixes_fn(a: Vec<u64>) -> (result: usize) | |
| requires | |
| 1 <= a.len() <= 200_000, | |
| forall|i: int| 0 <= i < a.len() ==> a[i] <= 1_000_000_000u64, | |
| ensures | |
| result as int == count_good_prefixes(a@, a.len() as int), | |
| { | |
| let mut sum: u64 = 0; | |
| let mut max_val: u64 = 0; | |
| let mut count: usize = 0; | |
| let mut i: usize = 0; | |
| while i < a.len() { | |
| let ai = a[i]; | |
| sum = sum + ai; | |
| if ai > max_val { | |
| max_val = ai; | |
| } | |
| if 2 * max_val == sum { | |
| count = count + 1; | |
| } | |
| i = i + 1; | |
| } | |
| count | |
| } | |
| } | |
| } | |