Description Difficulty: 2.0/5.0 URL: https://oj.leetcode.com/problems/min-stack/ Solution It looks like a non-trivial question, but the solution is trivial. The problem requires the MinStack to support four operations: pop(), top(), push(), and getMin() in constant time. The normal stack supports the first...
Description Difficulty: 1.5/5.0 URL: https://oj.leetcode.com/problems/copy-list-with-random-pointer/ Solution The most intuitive solution is to use a hash table to record the mapping relationship of the old nodes to the new nodes. After copying the list by setting the right next pointers, we...
Description Difficulty: 2.5/5.0 URL: https://oj.leetcode.com/problems/binary-tree-maximum-path-sum/ Solution The function maxPathSumHelper(pt, max_sum) return the maximum sum path sum of the path in the subtree rooted at pt, which ends/starts at pt. If the sum is less than 0, then it return zero...
Solution So the brute force solution is pretty straightforward: we go through each pair of numbers and check if their sum equals to the target. The time complexity is . The two solutions are less trivial, but with lower time...
Description Difficulty: 1.5/5.0 url: https://oj.leetcode.com/problems/reverse-linked-list-ii/ Solution class Solution { public: ListNode *reverseBetween(ListNode *head, int m, int n) { ListNode new_head(0); new_head.next = head; ListNode *p1 = &new_head; n -= m; while(--m) p1 = p1->next; ListNode *p2 = p1->next, *p3 =...