add: Pancake Sorting

Author: sidvishnoi

0969-pancake-sorting.rs

@@ -0,0 +1,53 @@
+struct Solution;
+
+// Two steps to bubble largest values to the end of list to sort:
+//  1. Bring value_to_sort to front of list by flipping list until it,
+//  2. Move it to the end of list by flipping rest of the list.
+//
+// Example: [2,1,{4},3]
+//  -> {4},1,2,3 -> [{3},2,1],4
+//  -> [1,2],{3},4
+impl Solution {
+    pub fn pancake_sort(mut a: Vec<i32>) -> Vec<i32> {
+        let mut result = Vec::new();
+
+        let largest_value = a.len() as i32;
+        for value_to_sort in (1..=largest_value).rev() {
+            let idx = a.iter().position(|&v| v == value_to_sort).unwrap() + 1;
+
+            if idx as i32 == value_to_sort {
+                // value_to_sort is in right place already
+                continue;
+            }
+
+            if idx != 1 {
+                // not in front of list already
+                result.push(idx as i32);
+                Self::flip(&mut a, idx);
+            }
+
+            result.push(value_to_sort);
+            Self::flip(&mut a, value_to_sort as usize);
+        }
+
+        result
+    }
+
+    fn flip(a: &mut Vec<i32>, k: usize) {
+        let mut i = 0;
+        let mut j = k - 1;
+        while i < j {
+            a.swap(i, j);
+            i += 1;
+            j -= 1;
+        }
+    }
+}
+
+fn main() {
+    assert_eq!(
+        vec![3, 4, 2, 3, 2],
+        Solution::pancake_sort(vec![3, 2, 4, 1])
+    );
+    assert_eq!(Vec::<i32>::new(), Solution::pancake_sort(vec![1, 2, 3]));
+}