Data commit

Task/Quickselect-algorithm/Rust/quickselect-algorithm.rust

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+// See https://en.wikipedia.org/wiki/Quickselect
+
+fn partition<T: PartialOrd>(a: &mut [T], left: usize, right: usize, pivot: usize) -> usize {
+    a.swap(pivot, right);
+    let mut store_index = left;
+    for i in left..right {
+        if a[i] < a[right] {
+            a.swap(store_index, i);
+            store_index += 1;
+        }
+    }
+    a.swap(right, store_index);
+    store_index
+}
+
+fn pivot_index(left: usize, right: usize) -> usize {
+    return left + (right - left) / 2;
+}
+
+fn select<T: PartialOrd>(a: &mut [T], mut left: usize, mut right: usize, n: usize) {
+    loop {
+        if left == right {
+            break;
+        }
+        let mut pivot = pivot_index(left, right);
+        pivot = partition(a, left, right, pivot);
+        if n == pivot {
+            break;
+        } else if n < pivot {
+            right = pivot - 1;
+        } else {
+            left = pivot + 1;
+        }
+    }
+}
+
+// Rearranges the elements of 'a' such that the element at index 'n' is
+// the same as it would be if the array were sorted, smaller elements are
+// to the left of it and larger elements are to its right.
+fn nth_element<T: PartialOrd>(a: &mut [T], n: usize) {
+    select(a, 0, a.len() - 1, n);
+}
+
+fn main() {
+    let a = vec![9, 8, 7, 6, 5, 0, 1, 2, 3, 4];
+    for n in 0..a.len() {
+        let mut b = a.clone();
+        nth_element(&mut b, n);
+        println!("n = {}, nth element = {}", n + 1, b[n]);
+    }
+}