Mergesort implementation in Rust

merge_sort.rs

fn merge_sort(to_sort: &Vec<i32>) -> Vec<i32>{
	if to_sort.len() == 0 {
		vec![]
	} else if to_sort.len() == 1 {
		vector_slice(to_sort,0,1)
	} else {
		let mid = to_sort.len() / 2;
		let first = &vector_slice(to_sort, 0, mid);
		let second = &vector_slice(to_sort, mid, to_sort.len());
		let first = &merge_sort(first);
		let second = &merge_sort(second);
		let result = merge(first, second);
		result
	}
}

fn vector_slice(vec: &Vec<i32>, start: usize, end: usize) -> Vec<i32> {
	let mut slice = Vec::with_capacity(vec.len());
	for i in start..end {
		slice.push(vec[i]);
	}
	slice
}

fn merge(a: &Vec<i32>, b: &Vec<i32>) -> Vec<i32>{
	let mut c = Vec::with_capacity(a.len() + b.len());
	let mut ai = 0;
	let mut bi = 0;
	loop {
		if bi >= b.len() {
			while ai < a.len() {
				c.push(a[ai]);
				ai += 1;
			}
			break;
		}
		if ai >= a.len() {
			while bi < b.len() {
				c.push(b[bi]);
				bi += 1;
			}
			break;
		}
		if a[ai] <= b[bi] {
			c.push(a[ai]);
			ai += 1;
		} else {
			c.push(b[bi]);
			bi += 1;
		}
	}
	c
}

fn test_merge_vectors() {
	let a = vec![1,3,5,7,9];
	let b = vec![2,4,6,8,10,11,12,13];
	let c = merge(&a, &b);
	assert_eq!(c, [1,2,3,4,5,6,7,8,9,10,11,12,13]);

	let a = vec![];
	let b = vec![2,4,6,8,10,11,12,13];
	let c = merge(&a, &b);
	assert_eq!(c, [2,4,6,8,10,11,12,13]);

	let a = vec![1,3,5,7,9];
	let b = vec![];
	let c = merge(&a, &b);
	assert_eq!(c, [1,3,5,7,9]);

	let a = vec![1];
	let b = vec![2,4,6,8,10,11,12,13];
	let c = merge(&a, &b);
	assert_eq!(c, [1,2,4,6,8,10,11,12,13]);

	let a = vec![];
	let b = vec![];
	let c = merge(&a, &b);
	assert_eq!(c, []);

	println!("All merging tests passed!");
}

fn test_merge_sort() {
	let to_sort = &vec![];
	assert_eq!(merge_sort(to_sort), vec![]);

	let to_sort = &vec![1,2];
	assert_eq!(merge_sort(to_sort), vec![1,2]);

	let to_sort = &vec![2,1];
	assert_eq!(merge_sort(to_sort), vec![1,2]);

	let to_sort = &vec![1];
	assert_eq!(merge_sort(to_sort), vec![1]);

	let to_sort = &vec![6,5,3,1,8,7,2,4];
	assert_eq!(merge_sort(to_sort), vec![1,2,3,4,5,6,7,8]);

	let to_sort = &vec![6,5,3,1,8,7,2,4,9,10,11,12,13];
	assert_eq!(merge_sort(to_sort), vec![1,2,3,4,5,6,7,8,9,10,11,12,13]);

	println!("All sorting tests passed!");
}

fn main() {
	println!("Merge Sort Test");
	test_merge_vectors();
	test_merge_sort();
}