Add quick sort.rs

Author: whbrown

Diff for: labocédai/src/lib.rs

@@ -208,5 +208,20 @@ mod tests {
             assert_eq!(merge_sort(&mut [1]), [1]);
         }
 
+        #[test]
+        fn test_quick_sort() {
+            assert_eq!(
+                quick_sort(&mut [29, 10, 14, 30, 37, 14, 18]),
+                [10, 14, 14, 18, 29, 30, 37]
+            );
+            assert_eq!(
+                quick_sort(&mut [-1, -2, 1, 0]),
+                [-2, -1, 0, 1]
+            );
+            assert_eq!(quick_sort(&mut []), []);
+            assert_eq!(quick_sort(&mut [1, 1, 1, 2, 1]), [1, 1, 1, 1, 2]);
+            assert_eq!(quick_sort(&mut [2, 1, 1, 1, 2]), [1, 1, 1, 2, 2]);
+            assert_eq!(quick_sort(&mut [1]), [1]);
+        }
     }
 }

Diff for: labocédai/src/sort.rs

@@ -78,3 +78,37 @@ pub fn merge_sort(nums: &[isize]) -> Vec<isize> {
     let right = merge_sort(&nums[midpoint..]);
     merge(&left, &right)
 }
+
+fn pivot_helper(nums: &mut [isize], start: usize, end: usize) -> usize {
+    /* selects a pivot and arranges all nums less than it to the left of it,
+    and greater than it to the right of it */
+    let pivot_idx = start;
+    let mut offset = start;
+    for i in start+1..=end {
+        if nums[i] < nums[pivot_idx] {
+            offset += 1;
+            nums.swap(i, offset);
+        }
+    }
+    nums.swap(pivot_idx, offset);
+    offset
+}
+
+pub fn quick_sort(nums: &mut [isize]) -> &mut [isize] {
+    fn sort(nums: &mut [isize], left: usize, right: usize) -> &mut [isize] {
+        if left < right  {
+            let pivot_idx = pivot_helper(nums, left, right);
+            // left
+            if pivot_idx > 0 {
+                sort(nums, left, pivot_idx - 1);
+            }
+            // right
+            sort(nums, pivot_idx+1, right);
+        }
+        nums
+    }
+    if nums.len() > 0 {
+        sort(nums, 0, nums.len() - 1);
+    }
+    nums
+}