Create remove-zero-sum-consecutive-nodes-from-linked-list.cpp

Author: kamyu104

C++/remove-zero-sum-consecutive-nodes-from-linked-list.cpp

@@ -0,0 +1,62 @@
+// Time:  O(n)
+// Space: O(n)
+
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode(int x) : val(x), next(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode* removeZeroSumSublists(ListNode* head) {
+        ListNode dummy(0);
+        auto curr = &dummy;
+        dummy.next = head;
+        int prefix = 0;
+        OrderedDict<int, ListNode*> lookup;
+        while (curr) {
+            prefix += curr->val;
+            auto node = curr;
+            if (lookup.count(prefix)) {
+                node = lookup[prefix];
+            }
+            while (lookup.count(prefix)) {
+                lookup.popitem();
+            }
+            lookup[prefix] = node;
+            node->next = curr->next;
+            curr = curr->next;
+        }
+        return dummy.next;
+    }
+
+private:
+    template<typename K, typename V>
+    class OrderedDict {
+    public:
+        bool count(const K& key) const {
+            return map_.count(key);
+        }
+        
+        V& operator[](const K& key) {
+            if (!map_.count(key)) {
+                list_.emplace_front();
+                list_.begin()->first = key;
+                map_[key] = list_.begin();
+            }
+            return map_[key]->second;
+        }
+
+        void popitem() {
+            auto del = list_.front(); list_.pop_front();
+            map_.erase(del.first);
+        }
+    
+    private:
+        list<pair<K, V>> list_;
+        unordered_map<K, typename list<pair<K, V>>::iterator> map_;
+    };
+};