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Diffstat (limited to 'other/max_twin_sum_list.cpp')
-rw-r--r-- | other/max_twin_sum_list.cpp | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/other/max_twin_sum_list.cpp b/other/max_twin_sum_list.cpp new file mode 100644 index 0000000..dd635e1 --- /dev/null +++ b/other/max_twin_sum_list.cpp @@ -0,0 +1,41 @@ +// 2130. Maximum Twin Sum of a Linked List +#include "leetcode.h" + +/* + * in a linked-list of size 'n', where 'n' is even, the i'th node (0-indexed) of + * the linked list is known as the twin of the 'n - 1 - i' node, if 0 <= i <= (n + * / 2) - 1. for example, if 'n = 4', then node 0 is the twin of node 3, and + * node 1 is the twin node of node 2. these are the only nodes with twins for 'n + * = 4'. the twin sum is defined as the sum of a node and its twin. given the + * 'head' of a linked list with even length, return the maximum twin sum of the + * linked list. + * + */ + +class Solution { +public: + int pairSum(ListNode *head) { + int ans = 0; + auto slow = head, fast = head; + while (fast != nullptr && fast->next != nullptr) { + fast = fast->next->next; + slow = slow->next; + } + slow = reverseList(slow); + while (slow != nullptr) { + ans = max(ans, slow->val + head->val); + slow = slow->next; + head = head->next; + } + return ans; + } + +private: + ListNode *reverseList(ListNode *curr, ListNode *prev = nullptr) { + while (curr != nullptr) { + swap(curr->next, prev); + swap(prev != nullptr ? prev->next : prev, curr); + } + return prev; + } +}; |