s0023

include/s0023_merge_k_sorted_lists.hpp

@@ -0,0 +1,21 @@
+#ifndef S0023_MERGE_K_SORTED_LISTS
+#define S0023_MERGE_K_SORTED_LISTS
+
+#include <vector>
+
+using namespace std;
+
+struct ListNode {
+  int val;
+  ListNode* next;
+  ListNode() : val(0), next(nullptr) {}
+  ListNode(int x) : val(x), next(nullptr) {}
+  ListNode(int x, ListNode* next) : val(x), next(next) {}
+};
+
+class Solution {
+ public:
+  ListNode* mergeKLists(vector<ListNode*>& lists);
+};
+
+#endif

src/s0023_merge_k_sorted_lists.cpp

@@ -0,0 +1,43 @@
+#include "s0023_merge_k_sorted_lists.hpp"
+
+ListNode *mergeTwoLists(ListNode *a, ListNode *b) {
+  if (a == nullptr) {
+    return b;
+  } else if (b == nullptr) {
+    return a;
+  }
+  ListNode dummy;
+  ListNode *tail = &dummy;
+  while (a != nullptr && b != nullptr) {
+    if (a->val > b->val) {
+      tail->next = b;
+      b = b->next;
+    } else {
+      tail->next = a;
+      a = a->next;
+    }
+    tail = tail->next;
+  }
+  if (a == nullptr) {
+    tail->next = b;
+  } else {
+    tail->next = a;
+  }
+  return dummy.next;
+}
+
+// 分治合并
+ListNode *merge(vector<ListNode*> &lists, int l, int r) {
+  if (l == r) {
+    return lists[l];
+  }
+  if (l > r) {
+    return nullptr;
+  }
+  int mid = (l + r) >> 1;
+  return mergeTwoLists(merge(lists, 1, mid), merge(lists, mid + 1, r));
+}
+
+ListNode* Solution::mergeKLists(vector<ListNode*>& lists) {
+  return merge(lists, 0, lists.size() - 1);
+}