49 lines
1.0 KiB
Rust
49 lines
1.0 KiB
Rust
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use std::clone::Clone;
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use std::cmp::PartialOrd;
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fn merge_count_inversions<T: Clone + PartialOrd + Copy + std::fmt::Debug>(
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a: Vec<T>,
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b: Vec<T>,
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) -> (Vec<T>, usize) {
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let mut r = vec![];
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let mut i = 0;
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let mut j = 0;
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let mut inversions = 0;
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while i < a.len() && j < b.len() {
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if a[i] < b[j] {
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r.push(a[i]);
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i += 1;
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} else {
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r.push(b[j]);
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j += 1;
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inversions += a.len() - i;
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}
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}
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while i < a.len() {
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r.push(a[i]);
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i += 1;
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}
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while j < b.len() {
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r.push(b[j]);
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j += 1;
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}
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return (r, inversions);
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}
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pub fn merge_sort_inversions<T: Clone + PartialOrd + Copy + std::fmt::Debug>(
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v: Vec<T>,
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) -> (Vec<T>, usize) {
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if v.len() <= 1 {
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return (v, 0);
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}
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let i = v.len() / 2;
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let (a, n) = merge_sort_inversions((&v[..i]).to_vec());
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let (b, m) = merge_sort_inversions((&v[i..]).to_vec());
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let (r, p) = merge_count_inversions(a, b);
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return (r, n + m + p);
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}
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