solve 23

Author: Zhang Xiaodong

src/solution/mod.rs

@@ -18,3 +18,4 @@ mod s0019_remove_nth_node_from_end_of_list;
 mod s0020_valid_parentheses;
 mod s0021_merge_two_sorted_lists;
 mod s0022_generate_parentheses;
+mod s0023_merge_k_sorted_lists;

src/solution/s0023_merge_k_sorted_lists.rs

@@ -0,0 +1,136 @@
+/**
+ * [23] 合并 K 个升序链表
+ *
+ * 给你一个链表数组，每个链表都已经按升序排列。
+ * 请你将所有链表合并到一个升序链表中，返回合并后的链表。
+ *  
+ * 示例 1：
+ * 输入：lists = [[1,4,5],[1,3,4],[2,6]]
+ * 输出：[1,1,2,3,4,4,5,6]
+ * 解释：链表数组如下：
+ * [
+ *   1->4->5,
+ *   1->3->4,
+ *   2->6
+ * ]
+ * 将它们合并到一个有序链表中得到。
+ * 1->1->2->3->4->4->5->6
+ *
+ * 示例 2：
+ * 输入：lists = []
+ * 输出：[]
+ *
+ * 示例 3：
+ * 输入：lists = [[]]
+ * 输出：[]
+ *
+ *  
+ * 提示：
+ *
+ * 	k == lists.length
+ * 	0 <= k <= 10^4
+ * 	0 <= lists[i].length <= 500
+ * 	-10^4 <= lists[i][j] <= 10^4
+ * 	lists[i] 按 升序 排列
+ * 	lists[i].length 的总和不超过 10^4
+ *
+ */
+pub struct Solution {}
+
+use crate::util::linked_list::{to_list, ListNode};
+
+// problem: https://leetcode.cn/problems/merge-k-sorted-lists/
+// discuss: https://leetcode.cn/problems/merge-k-sorted-lists/discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+
+use std::collections::BinaryHeap;
+
+impl PartialOrd for Box<ListNode> {
+    fn partial_cmp(&self, other: &Box<ListNode>) -> Option<std::cmp::Ordering> {
+        if self.val < other.val {
+            Some(std::cmp::Ordering::Greater)
+        } else if self.val == other.val {
+            Some(std::cmp::Ordering::Equal)
+        } else {
+            Some(std::cmp::Ordering::Less)
+        }
+    }
+}
+
+impl Ord for Box<ListNode> {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        if self.val < other.val {
+            std::cmp::Ordering::Greater
+        } else if self.val == other.val {
+            std::cmp::Ordering::Equal
+        } else {
+            std::cmp::Ordering::Less
+        }
+    }
+}
+
+// Definition for singly-linked list.
+// #[derive(PartialEq, Eq, Clone, Debug)]
+// pub struct ListNode {
+//   pub val: i32,
+//   pub next: Option<Box<ListNode>>
+// }
+//
+// impl ListNode {
+//   #[inline]
+//   fn new(val: i32) -> Self {
+//     ListNode {
+//       next: None,
+//       val
+//     }
+//   }
+// }
+impl Solution {
+    pub fn merge_k_lists(lists: Vec<Option<Box<ListNode>>>) -> Option<Box<ListNode>> {
+        let mut heap = BinaryHeap::new();
+        for p in lists {
+            if let Some(e) = p {
+                heap.push(e)
+            }
+        }
+        let mut dummy_head = Some(Box::new(ListNode { next: None, val: 0 }));
+        let mut curr = &mut dummy_head;
+        loop {
+            let mut p = heap.pop();
+            if p.is_none() {
+                break;
+            }
+            let mut p = p.unwrap();
+
+            let next = p.next.take();
+            if let Some(next) = next {
+                heap.push(next);
+            }
+            curr.as_mut().unwrap().next = Some(p);
+            curr = &mut curr.as_mut().unwrap().next;
+        }
+        dummy_head.unwrap().next
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_23() {
+        assert_eq!(
+            Solution::merge_k_lists(vec![
+                to_list(vec![1, 4, 5]),
+                to_list(vec![1, 3, 4]),
+                to_list(vec![2, 6]),
+            ],),
+            to_list(vec![1, 1, 2, 3, 4, 4, 5, 6])
+        );
+        assert_eq!(Solution::merge_k_lists(vec![]), None);
+        assert_eq!(Solution::merge_k_lists(vec![None]), None);
+    }
+}