[DaleSeo] WEEK 11 Solutions

reorder-list/DaleSeo.rs

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+// TC: O(n)
+// SC: O(1)
+impl Solution {
+    pub fn reorder_list(head: &mut Option<Box<ListNode>>) {
+        let mut len = 0;
+        let mut curr = head.as_ref();
+        while let Some(node) = curr {
+            len += 1;
+            curr = node.next.as_ref();
+        }
+        if len < 3 {
+            return;
+        }
+
+        let mut tail = {
+            let mut node = head.as_mut().unwrap();
+            for _ in 0..(len - 1) / 2 {
+                node = node.next.as_mut().unwrap();
+            }
+            node.next.take()
+        };
+
+        let mut reversed = None;
+        while let Some(mut n) = tail {
+            tail = n.next.take();
+            n.next = reversed;
+            reversed = Some(n);
+        }
+
+        let mut node = head.as_mut().unwrap();
+        while let Some(mut r) = reversed {
+            reversed = r.next.take();
+            r.next = node.next.take();
+            node.next = Some(r);
+            if reversed.is_none() {
+                break;
+            }
+            node = node.next.as_mut().unwrap().next.as_mut().unwrap();
+        }
+    }
+}