From ed62663069252a49bb3a1a00f4d0aaca41c63d2b Mon Sep 17 00:00:00 2001
From: Thomas Forgione <thomas@forgione.fr>
Date: Mon, 9 Jul 2018 16:35:57 +0200
Subject: [PATCH] Initial commit

---
 .gitignore |  3 ++
 Cargo.toml |  6 ++++
 src/lib.rs | 90 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 99 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Cargo.toml
 create mode 100644 src/lib.rs

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..aa085cd
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+Cargo.lock
+/target
+**/*.rs.bk
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..56302fb
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "partial-sort"
+version = "0.1.0"
+authors = ["Thomas Forgione <thomas@forgione.fr>"]
+
+[dependencies]
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..65c861b
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,90 @@
+use std::cmp::Ordering;
+
+pub fn partition_by<T, F: FnMut(&T, &T) -> Ordering>
+(slice: &mut [T], start: isize, end: isize, compare: &mut F) -> isize {
+
+    let mut i = start;
+    for j in start + 1 .. end + 1 {
+        if compare(&slice[j as usize], &slice[start as usize]) != Ordering::Greater {
+            i += 1;
+            slice.swap(i as usize, j as usize);
+        }
+    }
+    slice.swap(start as usize, i as usize);
+    i
+
+}
+
+pub fn quick_sort_by<T, F: FnMut(&T, &T) -> Ordering>
+(slice: &mut [T], start: isize, end: isize, compare: &mut F) {
+
+    if start < end {
+        let index = partition_by(slice, start, end, compare);
+        quick_sort_by(slice, start, index - 1, compare);
+        quick_sort_by(slice, index + 1, end, compare);
+    }
+
+}
+
+pub fn partial_sort_by<T, F: FnMut(&T, &T) -> Ordering>
+(slice: &mut [T], k: isize, compare: &mut F) {
+
+    let mut start = 0;
+    let mut end = slice.len() as isize - 1;
+
+    while end > start {
+
+        let index = partition_by(slice, start, end, compare);
+        let rank = index + 1;
+
+        if rank >= k {
+            end = index - 1;
+        } else if index - start > end - index {
+            quick_sort_by(slice, index + 1, end, compare);
+            end = index - 1;
+        } else {
+            quick_sort_by(slice, start, index - 1, compare);
+            start = index + 1;
+        }
+    }
+
+}
+
+/// Sorts the k first elements of the slice.
+///
+/// ```
+/// # extern crate partial_sort;
+/// # use partial_sort::partial_sort;
+/// let mut v = vec![5, 7, 4, 2, 8, 6, 1, 9, 0, 3];
+/// partial_sort(&mut v[..], 3);
+/// assert_eq!(v[0], 0);
+/// assert_eq!(v[1], 1);
+/// assert_eq!(v[2], 2);
+/// ```
+pub fn partial_sort<T: Ord>(slice: &mut [T], k: usize) {
+    partial_sort_by(slice, k as isize, &mut |x, y| x.cmp(y));
+}
+
+pub fn partial_sort_by_key<T, O: Ord, F: FnMut(&T) -> O>(slice: &mut [T], k: usize, key: &mut F) {
+    partial_sort_by(slice, k as isize, &mut |x, y| key(x).cmp(&key(y)));
+}
+
+#[cfg(test)]
+mod tests {
+
+    use partial_sort;
+
+    #[test]
+    fn partial_sort_test_1() {
+        let mut v = vec![5, 7, 4, 2, 8, 6, 1, 9, 0, 3];
+        partial_sort(&mut v[..], 7);
+        assert_eq!(v[0], 0);
+        assert_eq!(v[1], 1);
+        assert_eq!(v[2], 2);
+        assert_eq!(v[3], 3);
+        assert_eq!(v[4], 4);
+        assert_eq!(v[5], 5);
+        assert_eq!(v[6], 6);
+    }
+
+}